Demonstration set "Molecular Physics and Thermal Phenomena". Molecular physics. Thermal phenomena Molecular physics and thermal phenomena methodological guide
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1 State educational institution Lyceum 1547 National Research Nuclear University "MEPhI" Physical laboratory description of laboratory work for grades 8, 9, 10 and 11 of the Lyceum. Section Molecular Physics. Thermal phenomena. Moscow 2010 Edited by G.S. Bogdanova
2 Contents 3 OBSERVATION OF THE CURING OF AMORPHOUS SUBSTANCE. MEASUREMENT OF THE TEMPERATURE OF CRYSTALLIZATION OF SUBSTANCE. 4 STUDY OF THE PROPERTIES OF THE SUPERCOOLED LIQUID 5 STUDY OF THE ISOCHORAL PROCESS 7 STUDY OF THE ISOTHERMAL PROCESS. 9 STUDYING THE ISOBARITY PROCESS 10 2
3 1. OBSERVATION OF THE CURING OF AMORPHOUS SUBSTANCE. Equipment: a test tube with a yellow substance, a laboratory thermometer, a laboratory stand with a sleeve and a foot, a vessel with hot water(one per class), wrist watch... Content and method of performing the work. Amorphous substances do not have a specific melting point. As they heat up, they gradually soften, turning into a liquid that is less and less viscous. When cooled, this liquid continuously increases its viscosity until it solidifies into an amorphous solid. This is explained by the structural features of such substances. In amorphous substances, the molecules are also randomly arranged, as in liquids, and therefore their transition to a liquid state and back is not accompanied by a change in the molecular structure of the substance, but consists only in a continuous change in the mobility of molecules. Thus, the amorphous-solid state and the liquid state are not two different states of matter. A body made of an amorphous substance can formally correspond to the characteristics characteristic of solids- retain its shape and volume, but at the same time be a liquid, in which the mobility of molecules has significantly decreased due to cooling. The fact that amorphous substances, in contrast to crystalline ones, do not have a certain melting and crystallization temperature, can be seen by comparing the graphs of temperature changes with time, half-cantilevers when observing the cooling of crystalline and amorphous substances. In the presence of a teacher, a test tube with an amorphous yellow substance is immersed halfway into a vessel with hot water at a temperature of C. After the substance has warmed up sufficiently, make sure that there is liquid in the test tube. A thermometer is immersed in it and its readings are recorded with a time interval of one minute. When the temperature drops to 40 C, examine the substance in a test tube and make sure that it has solidified. The experiment is terminated. Build a graph of the dependence of the temperature of the substance on time and compare it with the graph constructed when performing the work "Measurement of the crystallization temperature of the substance". They are convinced that there is no crystallization process during the transition of an amorphous body from a liquid to a solid state. The order of the work. 1. Prepare a table for recording the measurement results: Time, min t, C 2. Determine the scale division of the thermometer. 3. Dip the test tube with the yellow substance in hot water and melt it. 4. Make sure the vial contains liquid. When the test tube is tilted in different directions, it can be seen that the shape of the substance in it changes depending on the slope, that is, it is not preserved, which is one of the differences between liquids and solids. 5. Place the thermometer in the tube and secure it to the tripod leg. 6. After the thermometer has stabilized, begin recording the temperature at one minute intervals. 7. When the temperature drops to 40 C, release the tube from the tripod leg and, tilting it in different directions, make sure that the substance is frozen. 8. Based on the measurements, build a graph of the dependence of the temperature of the substance in the test tube from time to time. If possible, compare it with the graph constructed during the work "Measurement of the crystallization temperature of a substance". 9. Using the graph, prove that there was an amorphous substance in the test tube. Control questions. 1. What is the difference between crystalline and amorphous solidification graphs? 2. What is the external difference between solids and liquids? 3
4 2. MEASUREMENT OF THE TEMPERATURE OF CRYSTALLIZATION OF SUBSTANCE. Equipment: a test tube with a green substance, a laboratory thermometer, a glass of hot water, a wristwatch. Content and method of performing the work. In a crystalline substance, atoms and molecules form an ordered packing and perform small vibrations around their equilibrium positions. As the body heats up, the speed of the oscillating particles increases along with the range of oscillations. The increase in the speed of movement of particles with increasing temperature is one of the basic laws of nature, which applies to matter in any state - solid, liquid or gaseous. At a certain temperature, the vibrations become so energetic that an ordered arrangement of particles becomes impossible - the crystal melts. With the onset of melting, the supplied heat is no longer spent on increasing the particle velocity, but on the destruction of the crystal lattice. Therefore, the rise in temperature is suspended. Subsequent heating is an increase in the speed of the liquid particles. In the case of crystallization from a melt, the above phenomena are observed in the reverse order: as the liquid cools, its particles slow down their chaotic motion; with a decrease in temperature to a certain value, the particles move so slowly that some of them, under the influence of the forces of attraction, begin to attach to one another, forming crystalline nuclei. Until all the substance crystallizes, the temperature will remain constant. This temperature is usually the same as the melting point. After all the substance passes into a solid state, the temperature begins to decrease again, which corresponds to the process of cooling the solid. Thus, the crystallization temperature of a substance can be determined by plotting a plot of temperature versus time. From the above it follows that this graph will have a characteristic section in the form of a segment parallel to the time axis. The temperature corresponding to this area will be the crystallization temperature of the given substance. The order of the work. 1. Prepare a table for recording the measurement results: Time, min t, C 2. Immerse the test tube with the test substance in the presence of a teacher in a vessel with water at a temperature of C and observe how the substance melts. 3. After all the substance has melted, transfer the test tube to a glass filled with about 150 ml of hot water, and place a thermometer in the melted substance. 4. From the moment when the temperature of the substance begins to decrease, record the thermometer readings at intervals of 1 minute. 5. Continuing to record the thermometer readings, observe the stage of transition of the substance into the solid state. 6. When cooling down to 45 C, stop measurements. Using the data obtained, build a graph of temperature versus time. 7. Using the graph, determine the crystallization temperature of the substance and the time during which the crystallization of the substance lasted. Control questions. 1. What is the difference between the graphs of temperature versus time during solidification of crystalline and amorphous substances? 2. How to determine the melting point of a crystalline body from the graph of the temperature change of a substance during heating from time to time? Additional task... 1. Pour about 400 ml of hot water into the vessel and immerse the test tube with the solidified crystalline substance into which the thermometer was previously melted. 2. Recording the readings of the thermometer with an interval of 1 minute, observe the change in the state of the substance when it is heated to 70 C. 3. Based on the measurements, build a graph of the dependence of the temperature of the substance on time and determine the melting point from it. 4. Compare the obtained values of the melting and crystallization temperatures of the substance. 4
5 3. STUDY OF PROPERTIES OF SUPERCOOLED LIQUID. Equipment: test tube, pink substance in a bag, laboratory thermometer, hot water vessel (one per class), glass beaker, wrist watch. Content and method of performing the work. If a crystalline substance in a liquid state is cooled, then at the moment when its temperature drops to the melting temperature, crystallization should begin. However, with a sufficiently rapid cooling of the liquid, crystallization does not always have time to occur and the substance turns out to be at a temperature that is below the melting point, retaining its liquid state. This phenomenon is called liquid hypothermia. In different liquids, hypothermia is achieved unequally easily. Some liquids can be supercooled tens of degrees below their crystallization temperature, others crystallize even with the slightest supercooling. The state of a supercooled liquid is unstable, as is the state of a supersaturated vapor or superheated liquid. Some liquids in a supercooled state are shaken enough to cause rapid crystallization. A supercooled liquid can also crystallize when a crystal of the same substance is introduced into it. Of the substances that are easily stored in a supercooled state, one can name hyposulfite, salol, vanillin. If a supercooled liquid begins to crystallize, having insignificant heat exchange with the surrounding bodies, then the energy released during this heats the resulting mixture of crystals and liquid. With not too strong supercooling, that is, when the temperature of the liquid at the moment of crystallization was not much lower than the melting point, the heat released can heat the entire system to the melting point, after which the crystallization rate will slow down and will depend on the rate at which the released heat will be absorbed surrounding bodies. The aim of the work is to plot the dependence of the temperature of a substance on time, determine the crystallization temperature from it, observe the growth of crystals in a supercooled liquid. The object of study is a pink substance in a test tube. In the presence of the teacher, the test tube is immersed halfway in hot water with a temperature of C. The substance will quickly melt. The test tube is transferred into a glass beaker without water or clamped in a tripod leg, a laboratory thermometer is inserted into it, and its readings are recorded with an interval of one minute. In order not to cause premature crystallization, the beaker with the test tube must be protected from jolts. The thermometer in the liquid must also be motionless. When the temperature drops to 35 C, the thermometer is raised and lowered several times inside the liquid. This effect is sufficient to initiate the crystallization process. Continuing to measure the temperature, observe the formation of crystals. The experiment ends after the substance, having crystallized, begins to cool down as a solid. The order of the work. 1. Prepare a table for recording the measurement results: Time, min t, C 2. Determine the scale division of the thermometer. 3.Crumble the substance in a sachet and transfer it to a test tube. 4. Place the test tube with the substance in a vessel with hot water. When the substance is completely melted, transfer the test tube to a glass beaker without water and place a thermometer in it. 5. After the thermometer readings are settled, start recording its readings at intervals of one minute. 6. When the temperature drops to 35 C, stir the liquid in the test tube with a thermometer, taking care not to damage the tip. 7. When the first crystals form, pay attention to their shape and growth rate. 8. Build a graph of the dependence of the temperature of the substance on time. 9. According to the schedule, determine: a) the crystallization temperature of the substance, b) the duration of the residence time of the substance in the state of a supercooled liquid, 5
6 c) the duration of the crystallization time of the substance. 10. After finishing work, melt the substance again, cool and pour into a bag. Attention! The substance left in the test tube, during long-term storage, can lead to its cracking. Control questions. 1. What state of matter is called a supercooled liquid? 2. How can a substance be removed from the state of a supercooled liquid? 6
7 4. RESEARCH OF THE ISOCHORAL PROCESS Equipment: transparent tube with taps, manometric tube, measuring tape, stand with foot, outer glass of the calorimeter, laboratory thermometer, measuring cylinder, vessel with warm water. Content and method of performing the work The aim of the work is to study the dependence of gas pressure on temperature during its isochoric cooling. It follows from Charles's law that if the volume of a certain amount of gas does not change, then the change in its pressure and temperature satisfies the condition: P 1 / T 2 = P2 / T2 (1), where P 1 and P 2 are the gas pressure in the initial and final states , a T 1 and T 2 is the temperature in these states. At the beginning of the experiment, the pressure and temperature of the gas in the heated state are determined. Then it is cooled at a constant volume and the pressure and temperature are determined again. After that, it is checked how much the change in these parameters corresponds to equality (1). The test gas is the air inside the transparent tube. To heat it, the tube is placed tightly loop to loop in the calorimeter glass. Before that, one of the taps is closed. Laying starts from the end with the closed tap and is carried out so that the end with the open tap is on top. Then warm water is poured into a glass. The water level should be no more than 5-10 mm above the open tap. When heated, the air in the hose will expand and bubbles will begin to come out of the tap. When the temperatures of air and water become equal, expansion will stop and bubbles will stop forming. After the last bubble has separated, the tap is closed. The state of the air in the hose at this moment is taken as the initial one and begins to determine its parameters - temperature and pressure. The temperature is determined by a thermometer according to the water temperature, and the pressure according to the indication of the class barometer is an aneroid. This way of measuring pressure is possible for the following reasons. Bubbles form until the air pressure in the tube equals the sum of the pressure of the atmosphere and the column of water above the tap. But since the water level above the tap, according to the conditions of the experiment, is only a few millimeters, the pressure of the water column can be neglected in comparison with the pressure of the atmosphere. Based on this, we can assume that in the initial state, the air pressure in the tube is equal to atmospheric pressure. Having measured the initial parameters of the air, it is transferred to another state by cooling to room temperature. The tube is removed from the calorimeter and hung in the form of a coil on the tripod leg. The tripod foot is preliminarily fixed on the rod at a height of about 35 cm from the table surface. A measuring cylinder is placed under the foot, into which ml of water is poured. The thermometer is also removed from the calorimeter. Then one of the taps is connected to a manometric tube. This is done in the following sequence. The free end of the tube is immersed to the bottom in a graduated cylinder. The upper part of the tube is slightly clamped in the tripod leg, but so that the inner channel is not completely blocked. Check again that the lower end of the tube is immersed in water. Only after these operations, the tube is connected to the tap using a connecting pipe. On contact with colder classroom air, the air in the large tube cools, its pressure drops, but the volume remains constant. If you open the tap, a pressure difference will appear at the ends of the manometric tube and water from the vessel will begin to be drawn up the tube until the pressure of the water column in it and the air pressure in the large tube equalize the atmospheric pressure. that is, until we are stupid by the equality: P at = P 2 + P in, where P B is the pressure in the tube, and P B is the pressure of the water column in the manometric tube. Hence P 2 = P at - P in. The height of the water column is used to determine its pressure and, knowing the pressure of the atmosphere, the pressure in the large tube after cooling P 2 is calculated. The temperature in the tube at this moment is equal to the air temperature in the classroom and is determined by a thermometer. Having obtained the values of P 1, P 2, T 1 and T 2, we find the ratio of the air pressure to its temperature in the heated and cooled state and check how much equality (1) is fulfilled under the conditions of the experiment. 7
8 Procedure for performing work 1. Prepare a table for recording the results of measurements and calculations: t 1, С Т 1, К Р 2, Pa t 2, С Т 2, К h, mm Р В, Pa Р 2, Pa Р 1 / T 1 Р 2 / Т 2 2. Using the thermometer reading, determine the air temperature in class t 2. 3. Put the tube into the outer cup of the calorimeter. 4. Fill the glass with warm water so that the open tap is submerged no more than 5-10 mm. 5.According to the separation of bubbles, determine the moment of equalization of the temperatures of water and air in the tube. 6.Use the water temperature to determine the temperature in the tube t 1. 7.Using an aneroid barometer, determine the air pressure in the tube P 1 = P at. 8.Close the tap, remove the tube from the glass and place it on the tripod as described above. 9.Connect the manometric tube to the valve by following the sequence of steps outlined in the previous section. 9. Smoothly open the tap and observe the rise in the water level in the manometric tube. At the moment when the air temperatures in the large tube and in the room become the same, the rise in the water level will stop. Then measure the difference in water levels in the tube and in the graduated cylinder - h. 11.Calculate the value of the pressure of the water column: Р В = ρgh, where ρ is the density of water, g is the acceleration of gravity, h is the level difference. 12.Calculate the air pressure in the tube after cooling Р 2 = P at - Р В 13.Convert the obtained temperature values into degrees of the Kelvin scale Т = t Calculate the ratios P 1 / T 1 and Р 2 / T Draw a conclusion about how much the result is corresponds to formula (1). Indicate the possible reasons for the discrepancy between experimental data and theory. Test questions 1. Why air cooling in the conducted experiment can be considered isochoric? 2. What conditions must be met for changes in gas parameters to comply with Charles's law 8
9 5. RESEARCH OF THE ISOTHERMAL PROCESS. Equipment: transparent tube with taps at the ends, measuring cylinder, measuring tape. Content and method of performing the work. The aim of the work is to check the relationship between the volume and pressure of a certain amount of gas during its isothermal compression. In accordance with the Boyle-Mariotte law, this ratio should have the form: V 1 P 1 = V 2 P 2 (1), where V 1 and V 2 are the volumes occupied by the gas, respectively, before and after compression, and P 1 and P 2 - his pressure. The object of study in the work is the air inside the transparent tube. Before compression, it has the following parameters. The pressure is equal to atmospheric. The volume is equal to the volume of the inner cavity of the tube. The temperature corresponds to the air temperature in the classroom. To compress the air in the tube, one of the valves is closed. The second tap is left open. The end of the tube with the tap open is immersed to the bottom of the measuring cylinder, which is pre-filled with water at room temperature, underfilling to the edge of mm. Through an open tap, water enters the tube and compresses the air until its pressure equals the external pressure. Thus, after compression, the air parameters will be as follows. The volume will be equal to the volume of the internal cavity minus the volume of water entering the tube. The pressure will increase by the value of the hydrostatic pressure of the water column in the cylinder. The temperature will not change. The volume of the inner cavity of the tube is determined by the product of its area cross section to the length. Since the cross-section of the tube is the same along its entire length, it is convenient to measure the air volume in conventional units. The unit of the length of the air column is taken as a conventional unit. So, in the initial state, the pressure is determined by the readings of the barometer - aneroid, and the volume with a measuring tape along the length of the inner cavity. To measure the pressure in the second state, the difference in water levels in the graduated cylinder and in the tube is measured - h. According to the formula for calculating the hydrostatic pressure of a liquid, the pressure of the water column is calculated: P in = ρgh, where ρ is the density of water. The air pressure in the second state will be equal to the sum of the atmospheric and hydrostatic pressures. To determine the volume of air in the second state, the length of the water column entering the tube is measured. The length of the water column is subtracted from the previously measured tube length. After completing the measurements, the products of pressure and air volume in the first and second states are found. Comparing the numbers obtained, a conclusion is made about the validity of the Boyle-Mariotte law. The order of the work. 1. Prepare a table for recording the results of measurements and calculations: l 1, mm Р 1, Pa Δl, mm l 2, mm h, mm Р В, Pa Р 2, Pa l 1 P 1 l 2 P 2 2. Measure the length of the air column in the tube l Close one valve and immerse the open end of the tube in the graduated cylinder to the bottom. 4. Measure the length of the water column entering the tube - Δl. 5. Measure the difference in water levels in the graduated cylinder and in the tube - h. 6. Calculate the length of the air column in the tube after compression 1 2 = Δl. 7. Calculate the hydrostatic pressure of the water P = ρgh. 8. Calculate the air pressure in the tube after compression P 2 = P 1 + P in. 9. Calculate the products l 1 P 1 and 1 2 P 2 and draw a conclusion about how accurately the change in the gas parameters in the experiment performed corresponds to the Boyle-Mariotte law. 10. Indicate the reasons that influenced the accuracy of the results. Control questions. 1. Why the process of air compression in this work can be considered isobaric? 2. What conditions must be met in order for changes in gas parameters to comply with the Boyle-Mariotte law? nine
10 6. STUDYING THE ISOBARITY PROCESS Equipment: a transparent tube with two taps at the ends, a laboratory thermometer, a measuring tape, an outer beaker of a calorimeter, a vessel with warm water, a vessel with cold water. Content and method of performing the work The purpose of the work is to check the relationship between the change in volume and temperature of a certain amount of gas during its isobaric cooling. In accordance with the Gay-Lussac law, this ratio should have the form: V 1 / T 1 = V 2 / T 2 (1), where V 1 and V 2 are the volumes occupied by a given mass of gas, respectively, before and after cooling, and T 1 and T 2 is its temperature. The investigated gas in this work is the air inside the transparent tube. To isolate the inner cavity of the tube from the external environment, special taps are fixed at the ends. Measurements of the volume and temperature of warm and cold air inside the tube are carried out in the following order. The tube is placed tightly, loop to loop, inside the calorimeter glass. The crane, which will be located near the bottom, is preliminarily closed. The top tap is left open. Then water heated to C is poured into the calorimeter. Water is poured so that an open tap would be immersed in it by no more than 5-10mm. As it warms up, the volume of air in the tube will increase and bubbles will come out of the open tap. At the moment when the air temperature equals the temperature of warm water, the release of bubbles will stop. This state of air in the tube is taken as the initial state. The air temperature in the initial state T 1 can be determined by measuring the temperature of the water in the glass. Its volume V 1 is equal to the volume of the inner cavity of the tube. After measuring the temperature of warm water, the air is transferred to a state with other parameters. To do this, close the tap, drain the warm water and fill the glass with cold water, making sure that its level above the top tap is the same as in the first part of the experiment. After that, the tap is opened again. During cooling, the air volume will decrease, and a certain amount of water will enter the tube through the open tap. When the temperatures of water and air become the same again (after 1-2 minutes), they begin to determine the parameters of the gas in a new state. The air temperature is again determined from the water temperature. To determine its volume after cooling, close the upper tap, remove the tube from the calorimeter and, while holding it vertically, shake it sharply several times. In this case, the drops of water that have fallen inside will merge and form an unbreakable column. By measuring the volume of this water column and subtracting it from the internal volume of the tube, the volume of air in the final state is determined. It is convenient to measure volumes in this work in conventional units along the length of the air or water column: the inner cavity of the tube has the shape of a cylinder and its volume is V = S l, but the cross-sectional area S does not change during the experiment, and in order not to measure this value, which, after substitution in equality (1), will still decrease, the volume is expressed in units of length (see Figures 1 and 2). The air pressure in the tube in the first and second parts of the experiment was equal to the sum of the atmospheric pressure and the pressure of a small column of water above the open tap. Since the level is warm and cold water did not change, then this amount did not change during the experiment, which means that the air pressure in the tube during its cooling remained constant, that is, the process proceeded isobaric. At the end of the work, the ratio of the volume of air to its temperature is compared before and after cooling. ten
11 Work order 1. Prepare a table for recording the results of measurements and calculations: l 1, cm t 1, CT 1, K Δl, cm l 2, cm t 2, CT 2, K l 1 / T 1 l 2 / T 2 2. Measure the length of the air column in the tube l 1 (Fig. 1). 3.Close one tap and place the coil-to-coil tube into the calorimeter glass. Leave the tap at the top end open. 4.Fill a glass with warm water and place a thermometer in it. 5. Observe the release of air bubbles from the open tap. As soon as it stops, determine and record the reading of the thermometer t 1 (C). 6.Close the tap, drain the warm water, fill the glass with cold water to the previous level and reopen the tap. 7.Wait one and a half - two minutes, determine and write down the thermometer reading t 2 (C). 8.Close the tap, drain the water, remove the hose from the glass, shake it and measure the length of the water column in it Δl (Fig. 2). 9.Calculate the length of the column of cooled air: l 2 = l 1 - Δl. 10.Translate the recorded thermometer readings into degrees Kelvin: T = t Calculate the ratios l 1 / T 1 and l 2 / T 1 and draw a conclusion about how accurately the change in gas parameters in this experiment corresponds to the Gay-Lussac law. 12. Indicate the reasons that influenced the accuracy of the results. Test questions 1. Why the process of air cooling in this work can be considered isobaric? 2. What conditions must be met in order to determine the parameters of the gas, it was possible to use the Gay-Lussac law? eleven
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Laboratory work 8 Determination of the ratio of the heat capacity of a gas at constant pressure to the heat capacity of a gas at a constant volume Purpose of the work: studying the laws of an ideal gas and determining empirically
Lesson on the topic: “Thermal motion. Temperature »THERMAL MOTION. TEMPERATURE We begin this academic year by studying a new section of physics devoted to thermal phenomena. Thermal phenomena include
Saturated and unsaturated vapors. Humidity. As noted in the first task, in a liquid (or solid) at any temperature there is a certain number of "fast" molecules, the kinetic energy of which is
Final test, Machine Science (Heat Engineering) 1. Ideal gas gave off the amount of heat 300 J and at the same time the internal energy of the gas decreased by 100 J. The work done by the gas is equal to 1) 400 J 2) 200
MOLECULAR PHYSICS AND THERMODYNAMICS Kirillov A.M., teacher of the gymnasium 44, Sochi (http://kirillandrey72.narod.ru/)
Ministry of Education and Science Russian Federation State educational institution of Higher professional education "UFA STATE OIL TECHNICAL UNIVERSITY"
Changes in physical quantities in processes, part 1 1. The temperature of the refrigerator of the ideal heat engine was reduced, leaving the heater temperature the same. The amount of heat received by the gas from the heater
Work 2.16 Study of the dependence of the viscosity of an amorphous substance on temperature and determination of the activation energy of its water molecules. Equipment: consistometer, stopwatch, test amorphous body, introduction
18.2 State diagram. Triple point. Phase transformations are determined by changes in temperature and pressure. For a visual representation of phase transformations, a state diagram is used, in which
Tasks for control work 2 Control work is carried out in chapters: "Heat machines", "Molecular-kinetic theory of ideal gas" and "Aggregate states of matter". If the student has completed everything
KALMYTSK STATE UNIVERSITY Department of General Physics Laboratory work 9 "Determination of the heat of transition of water into steam at boiling point" Laboratory 211 Laboratory work 9 "Determination of heat
MKT training tasks (A) What phenomenon most convincingly proves that there are repulsive forces between molecules?) Diffusion) Brownian motion) disorderly movement of molecules 4)
Individual task N 7 1.1. Two vessels of the same volume contain oxygen. In one vessel, the pressure P 1 = 2 MPa and the temperature T 1 = 800 K, in the other P 2 = 2.5 MPa, T 2 = 200 K. The vessels were connected by a tube
Experimental assignment. Observation of the cooling of water in the vessel, if the water is clean, if a thin layer of sunflower oil or milk is poured onto the surface of the water. Purpose of work: to learn how to measure the cooling rate
Ministry of Education and Science, Youth and Sports of Ukraine State Higher educational institution"National mining University"Methodological instructions for laboratory work. 3 DETERMINATION OF THE COEFFICIENT
2.3. FUNDAMENTALS OF THERMODYNAMICS Basic laws and formulas Thermodynamics investigates thermal properties gases, liquids and solids. A physical system in thermodynamics (it is usually called thermodynamic) is
DETERMINATION OF THE C P / C V RATIO FOR AIR BY THE KLEMAN-DESORM METHOD Accessories: complete experimental setup. Introduction. According to the first law of thermodynamics, the heat supplied to the thermodynamic
LABORATORY WORK 21 DETERMINATION OF SURFACE TENSION OF LIQUIDS The purpose of the work: measurement of surface tension of liquids by the method of separation of drops at room temperature. Equipment: dropper,
Compiled by: Yargaeva V.A. WORK. CONSTRUCTION OF THE FUSION CHART OF A TWO-COMPONENT SYSTEM Purpose of the work: to master thermal analysis: to record the cooling curves of pure components and binary mixtures of various
MEASURING THE VISCOSITY COEFFICIENT OF A LIQUID BY THE STOKS METHOD Methodological instructions for laboratory work MINISTRY OF EDUCATION AND SCIENCE OF THE RF NATIONAL RESEARCH TOMSK STATE
TASKS FOR INDIVIDUAL HOME JOB 5 (graph at the end of the file) 1. An air bubble at the bottom of a lake 16 m deep has a volume of 1.1 cm 3 The temperature at the bottom is 5 C, and at the surface 16 C. Determine
Work 22 Determination of the density of bulk and porous bodies Equipment: two identical vessels, liquid manometer, bulk or porous body Introduction As you know, the density of a substance ρ = m, (1) V where m is the mass
Virtual laboratory work 6 DETERMINATION OF THE RATIO OF MOLAR HEAT CAPACITIES C / C v FOR AIR (computer simulation) V. V. Monakhov, A. V. Kozhedub, A. V. Smirnov The purpose of the work is experimental determination
Laboratory work "Measuring the acceleration of gravity" Purpose of the work: to determine the acceleration of gravity using a thread pendulum. Devices and materials: tripod with clutch and foot; mass weight
17.3 Joule-Thomson effect If a gas expands adiabatically and does work, then it must cool, since the work it does is done by its internal energy. This was observed
PHYSICS Grade 8 Lesson topic: "Melting and solidification of bodies" Lesson objectives: Subject: to ensure the consolidation of basic concepts and the application of knowledge and methods of action on the topic; organize activities for independent
Molecular physics. Thermal phenomena
Experimental substantiation of the main provisions of the ICB:
Molecular kinetic theory- the doctrine of the structure and properties of matter, using the concept of the existence of atoms and molecules as the smallest particles of a chemical substance. The MKT is based on three assertions strictly proven through experiments:
Matter consists of particles - atoms and molecules, between which there are gaps;
These particles are in chaotic motion, the speed of which is influenced by temperature;
The particles interact with each other.
The fact that a substance really consists of molecules can be proved by determining their size. A drop of oil spreads over the surface of the water, forming a layer, the thickness of which is equal to the diameter of the molecule. A drop with a volume of 1 mm3 cannot spread out more than 0.6 m2:
There are also other ways to prove the existence of molecules, but there is no need to list them: modern devices (electron microscope, ion projector) allow you to see individual atoms and molecules.
Forces of interaction of molecules... a) the interaction is electromagnetic in nature; b) short-range forces are found at distances comparable to the size of molecules; c) there is such a distance when the forces of attraction and repulsion are equal (R0), if R> R0, then the forces of attraction prevail, if R The action of the forces of molecular attraction is revealed in the experiment with lead cylinders sticking together after cleaning their surfaces. Molecules and atoms in solid make random vibrations relative to the positions in which the forces of attraction and repulsion from the side of neighboring atoms are balanced. V liquids molecules not only vibrate about an equilibrium position, but also jump from one equilibrium position to an adjacent one, these jumps of molecules are the reason for the fluidity of the liquid, its ability to take the shape of a vessel. V gases usually, the distances between atoms and molecules are, on average, much larger than the size of molecules; repulsive forces at large distances do not act, therefore gases are easily compressed; there are practically no forces of attraction between gas molecules, therefore gases have the property of expanding indefinitely. The mass and size of the molecules. Avogadro's constant: Any substance consists of particles, therefore amount of substance it is considered to be proportional to the number of particles. The unit of the amount of a substance is mole. Moth is equal to the amount of matter in a system containing as many particles as there are atoms in 0.012 kg of carbon. The ratio of the number of molecules to the amount of substance is called Avogadro constant: Avogadro's constant is equal to />. It shows how many atoms or molecules are contained in one mole of a substance. The amount of a substance can be found as the ratio of the number of atoms or molecules of a substance to Avogadro's constant: Molar mass is called a value equal to the ratio of the mass of a substance to the amount of a substance: Molar mass can be expressed in terms of the mass of a molecule: For determining molecular masses you need to divide the mass of a substance by the number of molecules in it: Brownian motion: Brownian motion- thermal motion of particles suspended in a gas or liquid. The English botanist Robert Brown (1773 - 1858) in 1827 discovered the disorderly movement of solid particles visible in a microscope in a liquid. This phenomenon was called Brownian motion. This movement does not stop; with an increase in temperature, its intensity increases. Brownian motion is the result of pressure fluctuations (noticeable deviation from the average). The reason for the Brownian motion of a particle is that the impacts of liquid molecules on the particle do not cancel each other out. Ideal gas: In a rarefied gas, the distance between molecules is many times greater than their size. In this case, the interaction between molecules is negligible and the kinetic energy of the molecules is much higher than the potential energy of their interaction. To explain the properties of a substance in a gaseous state, instead of a real gas, its physical model is used - an ideal gas. The model assumes: the distance between molecules is slightly larger than their diameter; molecules - elastic balls; forces of attraction do not act between molecules; when molecules collide with each other and with the walls of the vessel, the forces are repulsive; the movement of molecules obeys the laws of mechanics. The basic equation of the ideal gas MKT: The basic equation of the MKT allows you to calculate the gas pressure if the mass of the molecule, the mean value of the square of the velocity, and the concentration of molecules are known. Ideal gas pressure lies in the fact that molecules in collisions with the walls of the vessel interact with them according to the laws of mechanics as elastic bodies. When a molecule collides with a vessel wall, the projection of the velocity vx of the velocity vector onto the OX axis, perpendicular to the wall, changes its sign to the opposite, but remains constant in absolute value. Therefore, as a result of collisions of a molecule with a wall, the projection of its momentum onto the OX axis changes from mv1x = -mvx to mv2x = mvx. A change in the momentum of a molecule upon collision with a wall causes a force F1 acting on it from the side of the wall. The change in the momentum of the molecule is equal to the momentum of this force: During the collision, according to Newton's third law, the molecule acts on the wall with a force F2 equal in magnitude to the force F1 and directed in the opposite direction. There are many molecules, and each of them transmits the same impulse to the wall upon collision. In a second, they transfer momentum />, where z is the number of collisions of all molecules with the wall, which is proportional to the concentration of molecules in the gas, the velocity of the molecules and the surface area of the wall: />. Only half of the molecules move to the wall, the rest move in reverse side: />. Then the total impulse transmitted to the wall in 1 second: />. According to Newton's second law, the change in the momentum of a body per unit time is equal to the force acting on it: Given that not all molecules have the same speed, the force acting on the wall will be proportional to the mean square of the speed. Since the molecules move in all directions, the mean squares of the velocity projections are equal. Therefore, the mean square of the projection of the speed: />; />. Then the gas pressure on the vessel wall is equal to: /> is the basic equation of the MKT. Denoting the average value of the kinetic energy of the translational motion of ideal gas molecules: />, we get Temperature and its measurement: The basic equation of the MKT for an ideal gas establishes a relationship between an easily measurable macroscopic parameter - pressure - with such microscopic parameters of a gas as the average kinetic energy and concentration of molecules. But, having measured only the pressure, we cannot find out either the average value of the kinetic energy of the molecules separately, or their concentration. Consequently, to find the microscopic parameters of a gas, measurements of some other physical quantity associated with the average kinetic energy of molecules are needed. This value is temperature. Any macroscopic body or a group of macroscopic bodies under constant external conditions spontaneously passes into a state of thermal equilibrium. Thermal equilibrium - it is a state in which all macroscopic parameters remain unchanged for an arbitrarily long time. Temperature characterizes the state of thermal equilibrium of a system of bodies: all bodies of the system, which are in thermal equilibrium with each other, have the same temperature. To measure temperature, you can use the change in any macroscopic value depending on temperature: volume, pressure, electrical resistance, etc. Most often, in practice, the dependence of the volume of liquid (mercury or alcohol) on temperature is used. When calibrating a thermometer, the temperature of melting ice is usually taken as the origin (0); the second constant point (100) is the boiling point of water at normal atmospheric pressure (Celsius scale). Since different liquids expand unevenly when heated, the scale set in this way will to some extent depend on the properties of the given liquid. Of course, 0 and 100 ° C will be the same for all thermometers, but 50 ° C will not be the same. Unlike liquids, all rarefied gases expand when heated in the same way and change their pressure in the same way when the temperature changes. Therefore, in physics, to establish a rational temperature scale, a change in the pressure of a certain amount of rarefied gas at a constant volume or a change in the volume of a gas at a constant pressure are used. This scale is sometimes called ideal gas temperature scale. At thermal equilibrium, the average kinetic energy of the translational motion of the molecules of all gases is the same. The pressure is directly proportional to the average kinetic energy of the translational motion of the molecules: />. In thermal equilibrium, if the pressure of a gas of a given mass and its volume are fixed, the average kinetic energy of gas molecules must have a strictly defined value, like the temperature. to. />, then />, or />. We denote />. The value of / increases with increasing temperature and does not depend on anything other than temperature. Therefore, it can be considered a natural measure of temperature. Absolute temperature scale: We will consider the value />, measured in energy units, directly proportional to the temperature />, expressed in degrees: />, where /> is the coefficient of proportionality. The coefficient />, in honor of the Austrian physicist L. Boltzmann is called Boltzmann constant. Therefore, />. The temperature determined by this formula cannot be negative. Therefore, the smallest possible value temperature is 0 if pressure or volume is zero. The limiting temperature at which the pressure of an ideal gas vanishes at a fixed volume or the volume of an ideal gas tends to zero at a constant pressure is called the absolute zero temperature. The English scientist W. Kelvin introduced an absolute temperature scale. Zero temperature on the Kelvin scale corresponds to absolute zero, and each unit of temperature on this scale is equal to a degree on the Celsius scale. The unit of absolute temperature in SI is called Kelvin:/>. Hence, absolute temperature is a measure of the average kinetic energy of molecular motion. Gas Molecule Velocity: Knowing the absolute temperature, one can find the average kinetic energy of gas molecules, and, consequently, the average square of their velocity. The square root of this quantity is called mean square velocity: Experiments to determine the velocities of molecules have proven the validity of this formula. One of the experiments was proposed by O. Stern in 1920. Ideal gas equation of state (Mendeleev - Clapeyron equation). Universal gas constant: Based on the dependence of the gas pressure on the concentration of its molecules and temperature, an equation can be obtained that connects all three macroscopic parameters: pressure, volume and temperature, which characterize the state of a given mass of a sufficiently rarefied gas. This equation is called the ideal gas equation of state. />, where /> is the universal gas constant /> for a given mass of gas, therefore PAGE_BREAK-- /> is the Clapeyron equation. Isothermal, isochoric and isobaric processes: The quantitative relationships between two gas parameters at a fixed value of the third parameter are called gas laws. And the processes proceeding with the unchanged value of one of the parameters are isoprocesses. Isothermal process- the process of changing the state of the thermodynamic system of macroscopic bodies at constant temperature. /> for /> For a gas of a given mass, the product of the gas pressure and its volume is constant if the gas temperature does not change.- Boyle's law - Mariotte. Isochoric process- the process of changing the state of the thermodynamic system of macroscopic bodies at constant volume. /> for /> For a gas of a given mass, the ratio of pressure to temperature is constant if the volume of the gas does not change... - Charles's law. Isobaric process- the process of changing the state of the thermodynamic system of macroscopic bodies at constant pressure. /> for /> For a gas of a given mass, the ratio of volume to temperature is constant if the gas pressure does not change... - Gay-Lussac's law. Internal energy: The internal energy of a macroscopic body is equal to the sum of the kinetic energies of the random motion of all molecules (or atoms) relative to the centers of mass of the body and the potential energies of interaction of all molecules with each other (but not with the molecules of other bodies). In any process in an isolated thermodynamic system, the internal energy remains unchanged. /> Internal energy of ideal gas. To calculate the internal energy of the ideal monatomic gas with mass /> it is necessary to multiply the average kinetic energy of one atom /> by the number of atoms />. Taking into account that />, we obtain the value of the internal energy of an ideal gas: If an ideal gas consists of more complex molecules than a monatomic one, then its internal energy is equal to the sum of the translational and rotational motion of the molecules. For diatomic gas: /> For polyatomic gas: /> For real gases, liquids and solids, the average potential energy of interaction of molecules is not equal to zero. For gases, it is much less than the average kinetic energy of molecules, but for solids and liquids it is comparable to it. The average potential energy of interaction of molecules depends on the volume of the substance, since when the volume changes, the average distance between the molecules changes. Hence, the internal energy in thermodynamics in the general case, along with the temperature, also depends on the volume. Quantity of heat: The process of transferring energy from one body to another without doing work is called heat exchange or heat transfer... Heat transfer occurs between bodies with different temperatures. When contact is established between bodies with different temperatures, part of the internal energy is transferred from a body with a higher temperature to a body with a lower temperature. The energy transferred to the body as a result of heat exchange is called the amount of warmth. Specific heat of a substance: If the heat transfer process is not accompanied by work, then on the basis of the first law of thermodynamics, the amount of heat is equal to the change in the internal energy of the body: />. The average energy of the random translational motion of molecules is proportional to the absolute temperature. The change in the internal energy of a body is equal to the algebraic sum of changes in the energy of all atoms or molecules, the number of which is proportional to the mass of the body, therefore, the change in internal energy and, therefore, the amount of heat is proportional to the mass and change in temperature: The proportionality factor in this equation is called specific heat of a substance... Specific heat shows how much heat is needed to heat 1 kg of a substance per 1 K. Work in thermodynamics: In mechanics, work is defined as the product of the modules of force and displacement and the cosine of the angle between them. The work is performed when a force acts on a moving body and is equal to a change in its kinetic energy. In thermodynamics, the movement of a body as a whole is not considered, it is about the movement of parts of a macroscopic body relative to each other. As a result, the volume of the body changes, and its speed remains equal to zero. Work in thermodynamics is defined in the same way as in mechanics, but it is equal to a change not in the kinetic energy of a body, but in its internal energy. When work is done (compression or expansion), the internal energy of the gas changes. The reason for this is as follows: during elastic collisions of gas molecules with a moving piston, their kinetic energy changes. Let's calculate the work of the gas during expansion. The gas acts on the piston with a force />, where /> is the gas pressure, and /> is the surface area /> of the piston. When the gas expands, the piston is displaced in the direction of the force /> by a small distance />. If the distance is small, then the gas pressure can be considered constant. Gas work is equal to: where /> is the change in the gas volume. In the process of expansion, the gas does positive work, since the direction of the force and the movement coincide. In the process of expansion, the gas gives up energy to the surrounding bodies. The work done by external bodies on the gas differs from the work of the gas only by the sign />, since the force /> acting on the gas is opposite to the force /> with which the gas acts on the piston, and is equal to it in absolute value (Newton's third law); and the movement remains the same. Therefore, the work of external forces is equal to: The first law of thermodynamics: The first law of thermodynamics is the law of conservation of energy, extended to thermal phenomena. Law of energy conservation: energy in nature does not arise from nothing and does not disappear: the amount of energy is invariable, it only passes from one form to another. In thermodynamics, bodies are considered, the position of the center of gravity of which practically does not change. The mechanical energy of such bodies remains constant, and only the internal energy can change. Internal energy can be changed in two ways: by heat transfer and by doing work. In the general case, the internal energy changes both due to heat transfer and due to the performance of work. The first law of thermodynamics is formulated precisely for such common cases: The change in the internal energy of the system during its transition from one state to another is equal to the sum of the work of external forces and the amount of heat transferred to the system: If the system is isolated, then no work is done on it and it does not exchange heat with the surrounding bodies. According to the first law of thermodynamics the internal energy of an isolated system remains unchanged. Taking into account that />, the first law of thermodynamics can be written as follows: The amount of heat transferred to the system is used to change its internal energy and to work on external bodies by the system.. The second law of thermodynamics: it is impossible to transfer heat from a colder system to a hotter one in the absence of other simultaneous changes in both systems or in the surrounding bodies. Application of the first law of thermodynamics to isoprocesses: At isochoric process the volume of gas does not change and therefore the work of the gas is zero. The change in internal energy is equal to the amount of transferred heat: At isothermal process the internal energy of an ideal gas does not change. All the amount of heat transferred to the gas is used to perform the work: At isobaric process the amount of heat transferred to the gas goes to change its internal energy and to perform work at constant pressure. Adiabatic process: Adiabatic process- process in a thermally insulated system. Consequently, the change in internal energy during the adiabatic process occurs only due to the performance of work: Since the work of external forces during compression is positive, the internal energy of the gas during adiabatic compression increases, and its temperature rises. During adiabatic expansion, the gas performs work due to a decrease in its internal energy; therefore, the gas temperature decreases during adiabatic expansion. The principle of operation of heat engines: A heat engine is a motor that produces mechanical work due to the energy released during the combustion of fuel. Some types of heat engines: Steam engine; steam turbine; internal combustion engine; jet engine. Physical fundamentals the work of all heat engines is the same. A heat engine consists of three main parts: a heater, a working medium, and a refrigerator. The process of work of the heat engine: The working fluid is brought into contact with the heater (/> - high), so the working fluid receives from the heater />. Due to this amount of heat, the working fluid performs mechanical work. Then the working fluid is brought into contact with the refrigerator (/> - low), so the working fluid gives off heat to the refrigerator. Thus, it returns to its original state. Now the working fluid is brought into contact with the heater and everything happens all over again. Consequently, a heat engine is of periodic action, that is, in this machine, the body performs a closed process - a cycle. For each cycle, the working body does work /> or /> The efficiency is usually expressed as a percentage: Heat engine efficiency and its maximum value: At the beginning of the 19th century, the French engineer Sadi Carnot investigated ways to improve the efficiency of heat engines. He came up with a cycle that should make an ideal gas in some heat engine, such that the maximum possible efficiency is obtained. The Carnot cycle consists of two isotherms and two adiabats. The ideal gas is brought into contact with a heater and allowed to expand isothermally, that is, at the temperature of the heater. When the expanded gas passes into state 2, it is insulated from the heater and given the opportunity to expand adiabatically, that is, the gas does work due to the loss of its internal energy. Expanding adiabatically, the gas is cooled until its temperature is equal to the temperature of the refrigerator (state 3). The gas is now brought into contact with a condenser and compressed isothermally. Gas is given to the refrigerator />. The gas goes into state 4. Then the gas is insulated from the refrigerator and compressed adiabatically. In this case, the gas temperature increases and reaches the heater temperature. The process is repeated from the beginning. Formula for calculating the efficiency of an ideal heat engine operating according to the Carnot cycle with an ideal gas. Carnot showed that the efficiency of any other heat engine (that is, with a different working fluid or operating in a different cycle) will be less than the efficiency of the Carnot cycle. In practice, machines operating according to the Carnot cycle are not used, but the formula (*) allows you to determine the maximum efficiency at the given temperatures of the heater and refrigerator. Obviously, to increase the efficiency, it is necessary to lower the temperature of the refrigerator and increase the temperature of the heater. It is artificially unprofitable to lower the temperature of the refrigerator, as it requires additional energy consumption. It is also possible to increase the temperature of the heater up to a certain limit, since various materials have different heat resistance at high temperatures... However, the Carnot formula showed that there are unused reserves for increasing the efficiency, since the practical efficiency is very different from the efficiency of the Carnot cycle. Continuation Heat engines and nature conservation
Evaporation and condensation, saturated and unsaturated vapors: The uneven distribution of the kinetic energy of the thermal motion of molecules leads to the fact that at any temperature the kinetic energy of some molecules of a liquid or solid can exceed the potential energy of their binding with the rest of the molecules. Evaporation is a process in which molecules fly out from the surface of a liquid or solid, the kinetic energy of which exceeds the potential energy of the interaction of molecules. Evaporation is accompanied by the cooling of the liquid, since the molecules with high kinetic energy leave the liquid, and the internal energy of the liquid decreases. The escaped molecules begin to move randomly in the thermal motion of the gas; they can either permanently move away from the surface of the liquid, or return to the liquid again. This process is called condensation. Evaporation of a liquid in a closed vessel at a constant temperature leads to a gradual increase in the concentration of molecules of the evaporating substance in the gaseous state. Some time after the beginning of the evaporation process, the concentration of the substance in the gaseous state reaches such a value at which the number of molecules returning to the liquid per unit time becomes equal to the number of molecules leaving the surface of the liquid during the same time. A dynamic equilibrium is established between the processes of evaporation and condensation of a substance. A substance in a gaseous state that is in dynamic equilibrium with a liquid is called saturated steam... Steam located at a pressure below the pressure of saturated steam is called unsaturated. When saturated vapor is compressed, the concentration of vapor molecules increases, the equilibrium between the processes of evaporation and condensation is violated, and part of the vapor turns into liquid. With the expansion of saturated vapor, the concentration of its molecules decreases and part of the liquid turns into vapor. Thus, the concentration of saturated steam remains constant regardless of the volume. Since the gas pressure is proportional to the concentration and temperature (/>), the saturated vapor pressure at constant temperature does not depend on the volume. The intensity of the evaporation process increases with increasing temperature of the liquid. Therefore, a dynamic equilibrium between evaporation and condensation with increasing temperature is established at high concentrations of gas molecules. The pressure of an ideal gas at a constant concentration of molecules increases in direct proportion to the absolute temperature. Since the concentration of molecules in saturated steam increases with increasing temperature, the pressure of saturated steam increases faster with increasing temperature than the pressure of an ideal gas with a constant concentration of molecules. That is the saturated vapor pressure increases not only due to an increase in the temperature of the liquid, but also due to an increase in the concentration of vapor molecules. The main difference in the behavior of ideal gas and saturated steam is that when the temperature of the steam in a closed vessel changes (or when the volume changes at a constant temperature), the mass of the steam changes. The dependence of the boiling point of liquid on pressure: As the temperature rises, the rate of evaporation of the liquid increases, and at a certain temperature, the liquid begins to boil. When boiling, rapidly growing vapor bubbles are formed throughout the volume of the liquid, which float to the surface. The boiling point of the liquid remains constant. Dissolved gases are always present in the liquid, which are released at the bottom and walls of the vessel. The vapors of the liquid inside the bubbles are saturated. As the temperature rises, the saturated vapor pressure increases and the bubbles increase in size. Under the action of the buoyancy force, they float to the surface. The dependence of the saturated vapor pressure on temperature explains why the boiling point of a liquid depends on the pressure on its surface. A vapor bubble can grow when the pressure of saturated vapor inside it slightly exceeds the pressure in the liquid, which is the sum of the air pressure on the surface of the liquid (external pressure) and the hydrostatic pressure of the liquid column. Boiling begins at a temperature at which the pressure of the saturated vapor in the bubbles is equal to the pressure in the liquid. The higher the external pressure, the higher the boiling point. Each liquid has its own boiling point, which depends on the saturated vapor pressure. the higher the saturated vapor pressure, the lower the boiling point of the corresponding liquid, since at lower temperatures the saturated vapor pressure becomes equal to atmospheric. With an increase in the temperature of the liquid, the pressure of the saturated vapor increases and at the same time its density increases. The density of a liquid in equilibrium with its vapor, on the contrary, decreases due to the expansion of the liquid upon heating. If in one figure we draw the curves of the dependence of the density of a liquid and the density of its saturated vapor on temperature, then for a liquid the curve will go down, and for steam - up. At a certain temperature, both curves merge, that is, the density of the liquid becomes equal to the density of the vapor. The critical temperature is the temperature at which the differences in physical properties between the liquid and its saturated vapor disappear. At temperatures above critical, the substance does not turn into a liquid at any pressure. Air humidity: Atmospheric air is a mixture various gases and water vapor. Each of the gases contributes to the total pressure produced by the air on the bodies in it. The pressure that water vapor would produce if all other gases were absent is called the partial pressure of water vapor. Relative air humidity /> is the ratio of the partial pressure /> water vapor contained in the air at a given temperature to the pressure /> saturated vapor at the same temperature, expressed as a percentage: Since the pressure of the saturated vapor is lower, the lower the temperature, then when the air is cooled, the water vapor in it becomes saturated at a certain temperature. The temperature /> at which the water vapor in the air becomes saturated is called dew point. The dew point can be used to find the water vapor pressure in the air. It is equal to the saturated vapor pressure at a temperature equal to the dew point. The relative humidity of the air can be determined from the values of the vapor pressure in the air and the saturated vapor pressure at a given temperature. Crystalline and amorphous bodies: Amorphous bodies are called, the physical properties of which are the same in all directions. Amorphous bodies are isotropic- they do not have a strict order in the arrangement of atoms. Examples of amorphous bodies are pieces of hardened resin, amber, glass. Solids in which atoms or molecules are arranged in an orderly manner and form a periodically repeating internal structure are called crystals. Physical properties crystalline bodies are not the same in different directions, but coincide in parallel directions. This property of crystals is called anisotropy. The anisotropy of the mechanical, thermal, electrical, and optical properties of crystals is explained by the fact that with an ordered arrangement of atoms, molecules or ions, the forces of interaction between them and the interatomic distances are not the same in different directions. Crystalline bodies are divided into single crystals and polycrystals... Monocrystals sometimes possess geometrically the correct form, but the main feature of a single crystal is a periodically repeating internal structure throughout its entire volume. A polycrystalline body is a collection of chaotically oriented small crystals, crystallites, fused together with each other. Each small single crystal of a polycrystalline body is anisotropic, but a polycrystalline body is isotropic. Mechanical properties of solids: Let us consider the mechanical properties of a solid by the example of tensile deformation. In any section of a deformed body, elastic forces act, preventing the breaking of this body into parts. Mechanical stress called the ratio of the modulus of elasticity to the cross-sectional area of the body: At small deformations, the stress /> is directly proportional to the relative elongation /> (section OA). This dependence is called Hooke's law: />, where /> is Young's modulus. />, We denote />, then /> Hooke's law is fulfilled only at small deformations, and, therefore, at stresses not exceeding a certain limit. The maximum voltage /> at which Hooke's law is still satisfied is called proportional limit. If the load is increased, then the deformation becomes nonlinear, the stress ceases to be directly proportional to the relative elongation. Nevertheless, with small nonlinear deformations after removing the load, the shape and size of the body are practically restored (section AB). The maximum stress at which noticeable permanent deformations do not yet occur (the relative permanent deformation does not exceed 0.1%) is called elastic limit />. If the external load is such that the stress in the material exceeds the elastic limit, then after the load is removed, the body remains deformed. At a certain stress value corresponding to point C in the diagram, the elongation increases practically without increasing the load. This phenomenon is called flowability of material(section CD). Further, with increasing deformation, the stress curve begins to increase slightly and reaches a maximum at point E. Then the stress drops sharply and the body collapses. The rupture occurs after the voltage reaches a maximum value />, called ultimate strength. Elastic deformations: In case of elastic deformations, the size and shape of the body are restored when the load is removed. « Physics - Grade 10 " Let's give general idea about the meaning and meaning of what you will now begin to study. Macroscopic bodies. We live in a world of macroscopic bodies. Our body is also a macroscopic body. In physics, macroscopic bodies are large bodies consisting of a huge number of molecules. Gas in a cylinder, water in a glass, grain of sand, stone, steel rod, Earth are all examples of macroscopic bodies (Figure 7.7). Mechanics and mechanical movement. In Newtonian mechanics, they deal with the mechanical movement of macroscopic bodies - the movement of some bodies relative to others in space over time. Mechanics studies the movement of bodies, but it is not able to explain why there are solid, liquid and gaseous bodies and why these bodies can pass from one state to another. Investigation of the internal properties of bodies is not included in the task of mechanics. In mechanics, they speak of forces as the causes of changes in the velocities of bodies, but the nature of these forces, their origin is not clarified. It remains unclear why elastic forces appear when bodies are compressed, why friction occurs. The mechanic of Newton does not give answers to many, very many questions. All this was well understood by Newton himself. Significant words belong to him: “I do not know what I appear to the world; it seems to me myself that I was only a boy playing on the seashore and having fun by finding smoother stones or a more beautiful shell than usual, while the Great Ocean of Truth lay before me completely unsolved. " Thermal phenomena. After mechanical movement, the most noticeable phenomena are associated with the heating or cooling of bodies, with a change in their temperature. These phenomena are called thermal. Mechanical movement does not cause any significant changes in the body, unless catastrophic collisions occur. But heating or cooling the body can change it beyond recognition. Strongly heating transparent, but still visible water, we turn it into invisible vapor. Strong chilling will turn the water into a block of ice. If you think about it, these phenomena are mysterious and worthy of amazement. We are not surprised because we are accustomed to them since childhood. It is necessary to find laws that could explain the changes in bodies when the bodies themselves are stationary and when, from the point of view of mechanics, nothing happens to them. These laws describe a special kind of motion of matter - thermal motion, inherent in all macroscopic bodies, regardless of whether they move in space or not. Thermal motion of molecules. All bodies are made up of atoms and molecules. The movement of molecules is chaotic due to the fact that their number in the bodies that surround us is immeasurably large. Each molecule constantly changes its speed when colliding with other molecules. As a result, its trajectory turns out to be extremely confusing, the movement is chaotic, incomparably more chaotic than the movement of ants in a ruined anthill. The disorderly movement of a huge number of molecules is qualitatively different from the ordered mechanical movement of bodies. It is a special type of motion of matter with its own special properties. These properties will be discussed later. The significance of thermal phenomena. The habitual appearance of our planet exists and can exist only in a fairly narrow temperature range. If the temperature exceeded 100 ° C, then at normal atmospheric pressure there would be no rivers, seas and oceans on the Earth, there would be no water at all. All the water would turn into steam. And if the temperature dropped by several tens of degrees, the oceans would turn into huge glaciers. Even a change in temperature by only 20-30 ° C with the change of seasons changes the entire appearance of the planet at mid-latitudes. With the onset of spring, nature begins to awaken. Forests dress with foliage, meadows begin to turn green. In winter, plant life stops. A thick layer of snow covers the Earth's surface. Even narrower temperature ranges are necessary to maintain the life of warm-blooded animals. The temperature of animals and humans is maintained by the internal mechanisms of thermoregulation at a strictly defined level. It is enough for the temperature to rise by a few tenths of a degree, and we already feel unhealthy. A change in temperature by several degrees leads to the death of organisms. Therefore, it is not surprising that thermal phenomena have attracted the attention of people since ancient times. The ability to produce and maintain fire made a person relatively independent from temperature fluctuations. environment... This was one of the greatest inventions of humanity. A change in temperature affects all properties of bodies. So, when heated or cooled, the dimensions of solids and the volumes of liquids change. The mechanical properties of bodies, for example, elasticity, change significantly. A piece of rubber tube will survive if you hit it with a hammer. But when cooled to temperatures below -100 ° C, the rubber becomes brittle, like glass, and a light impact breaks the rubber tube into small pieces. Only after heating does the rubber regain its elastic properties. In addition to mechanical properties, when the temperature changes, other properties of bodies also change, for example, resistance to electric current, magnetic properties, etc. permanent magnet, then it will cease to attract iron objects. All of the above and many other thermal phenomena obey certain laws. The discovery of the laws of thermal phenomena makes it possible to apply these phenomena with maximum benefit in practice and in technology. Modern heat engines, gas liquefaction plants, refrigerators and many other devices are designed on the basis of these laws. Molecular kinetic theory. Even ancient philosophers guessed that warmth is a kind of internal movement. But only in the 18th century. consistent molecular kinetic theory. MV Lomonosov made a great contribution to the development of the molecular kinetic theory. He viewed heat as the rotational motion of body particles. The goal of the molecular kinetic theory is to explain the properties of macroscopic bodies and thermal processes occurring in them, based on the idea that all bodies consist of separate, randomly moving particles. Molecular kinetic theory Thermal phenomena in molecular physics. The forces of interaction of molecules, their mass and size. The reason for the Brownian motion of the particle. Ideal gas pressure. Temperature Thermal equilibrium concept. Isothermal process Isochoric process Isobaric process Internal energy Internal energy of ideal gas. Ideal gas temperature scale. Quantity of heat The first law of thermodynamics The second law of thermodynamics Specific heat of a substance Heat engines and nature conservation. Experimental substantiation of the main provisions of the ICB: Molecular kinetic theory- the doctrine of the structure and properties of matter, using the concept of the existence of atoms and molecules as the smallest particles of a chemical substance. The MKT is based on three assertions strictly proven through experiments: Matter consists of particles - atoms and molecules, between which there are gaps; These particles are in chaotic motion, the speed of which is influenced by temperature; The particles interact with each other. The fact that a substance really consists of molecules can be proved by determining their size. A drop of oil spreads over the surface of the water, forming a layer, the thickness of which is equal to the diameter of the molecule. A drop with a volume of 1 mm 3 cannot spread out more than 0.6 m 2: There are also other ways to prove the existence of molecules, but there is no need to list them: modern devices (electron microscope, ion projector) allow you to see individual atoms and molecules. Forces of interaction of molecules... a) the interaction is electromagnetic in nature; b) short-range forces are found at distances comparable to the size of molecules; c) there is such a distance when the forces of attraction and repulsion are equal (R 0), if R> R 0, then the forces of attraction prevail, if R The action of the forces of molecular attraction is revealed in the experiment with lead cylinders sticking together after cleaning their surfaces. Molecules and atoms in solid make random vibrations relative to the positions in which the forces of attraction and repulsion from the side of neighboring atoms are balanced. V liquids molecules not only vibrate about an equilibrium position, but also jump from one equilibrium position to an adjacent one, these jumps of molecules are the reason for the fluidity of the liquid, its ability to take the shape of a vessel. V gases usually, the distances between atoms and molecules are, on average, much larger than the size of molecules; repulsive forces at large distances do not act, therefore gases are easily compressed; there are practically no forces of attraction between gas molecules, therefore gases have the property of expanding indefinitely. The mass and size of the molecules. Avogadro's constant: Any substance consists of particles, therefore amount of substance it is considered to be proportional to the number of particles. The unit of the amount of a substance is mole. Moth is equal to the amount of matter in a system containing as many particles as there are atoms in 0.012 kg of carbon. The ratio of the number of molecules to the amount of substance is called Avogadro constant: Avogadro's constant is. It shows how many atoms or molecules are contained in one mole of a substance. The amount of a substance can be found as the ratio of the number of atoms or molecules of a substance to Avogadro's constant: Molar mass is called a value equal to the ratio of the mass of a substance to the amount of a substance: Molar mass can be expressed in terms of the mass of a molecule: For determining molecular masses you need to divide the mass of a substance by the number of molecules in it: Brownian motion: Brownian motion- thermal motion of particles suspended in a gas or liquid. The English botanist Robert Brown (1773 - 1858) in 1827 discovered the disorderly movement of solid particles visible in a microscope in a liquid. This phenomenon was called Brownian motion. This movement does not stop; with an increase in temperature, its intensity increases. Brownian motion is the result of pressure fluctuations (noticeable deviation from the average). The reason for the Brownian motion of a particle is that the impacts of liquid molecules on the particle do not cancel each other out. Ideal gas: In a rarefied gas, the distance between molecules is many times greater than their size. In this case, the interaction between molecules is negligible and the kinetic energy of the molecules is much higher than the potential energy of their interaction. To explain the properties of a substance in a gaseous state, instead of a real gas, its physical model is used - an ideal gas. The model assumes: the distance between molecules is slightly larger than their diameter; molecules - elastic balls; forces of attraction do not act between molecules; when molecules collide with each other and with the walls of the vessel, the forces are repulsive; the movement of molecules obeys the laws of mechanics. The basic equation of the ideal gas MKT: The basic equation of the MKT allows you to calculate the gas pressure if the mass of the molecule, the mean value of the square of the velocity, and the concentration of molecules are known. Ideal gas pressure lies in the fact that molecules in collisions with the walls of the vessel interact with them according to the laws of mechanics as elastic bodies. When a molecule collides with a vessel wall, the projection of the velocity v x of the velocity vector onto the OX axis, perpendicular to the wall, changes its sign to the opposite, but remains constant in absolute value. Therefore, as a result of collisions of a molecule with a wall, the projection of its momentum onto the OX axis changes from mv 1x = -mv x to mv 2x = mv x. A change in the momentum of a molecule upon collision with a wall causes a force F 1 acting on it from the side of the wall. The change in the momentum of the molecule is equal to the momentum of this force: During the collision, according to Newton's third law, the molecule acts on the wall with a force F 2 equal in magnitude to the force F 1 and directed oppositely. There are many molecules, and each of them transmits the same impulse to the wall upon collision. For a second, they transfer an impulse, where z is the number of collisions of all molecules with the wall, which is proportional to the concentration of molecules in the gas, the velocity of the molecules and the surface area of the wall:. Only half of the molecules move to the wall, the rest move in the opposite direction:. Then the total impulse transmitted to the wall in 1 second: Given that not all molecules have the same speed, the force acting on the wall will be proportional to the mean square of the speed. Since the molecules move in all directions, the mean squares of the velocity projections are equal. Therefore, the mean square of the projection of the speed:; ... Then the gas pressure on the vessel wall is equal to: Denoting the average value of the kinetic energy of the translational motion of ideal gas molecules: We get Temperature and its measurement: The basic equation of the MKT for an ideal gas establishes a relationship between an easily measurable macroscopic parameter - pressure - with such microscopic parameters of a gas as the average kinetic energy and concentration of molecules. But, having measured only the pressure, we cannot find out either the average value of the kinetic energy of the molecules separately, or their concentration. Consequently, to find the microscopic parameters of a gas, measurements of some other physical quantity associated with the average kinetic energy of molecules are needed. This value is temperature. Any macroscopic body or a group of macroscopic bodies under constant external conditions spontaneously passes into a state of thermal equilibrium. Thermal equilibrium - it is a state in which all macroscopic parameters remain unchanged for an arbitrarily long time. Temperature characterizes the state of thermal equilibrium of a system of bodies: all bodies of the system, which are in thermal equilibrium with each other, have the same temperature. To measure temperature, you can use the change in any macroscopic value depending on temperature: volume, pressure, electrical resistance, etc. Most often, in practice, the dependence of the volume of liquid (mercury or alcohol) on temperature is used. When calibrating a thermometer, the temperature of melting ice is usually taken as the origin (0); the second constant point (100) is the boiling point of water at normal atmospheric pressure (Celsius scale). Since different liquids expand unevenly when heated, the scale set in this way will to some extent depend on the properties of the given liquid. Of course, 0 and 100 ° C will be the same for all thermometers, but 50 ° C will not be the same. Unlike liquids, all rarefied gases expand when heated in the same way and change their pressure in the same way when the temperature changes. Therefore, in physics, to establish a rational temperature scale, a change in the pressure of a certain amount of rarefied gas at a constant volume or a change in the volume of a gas at a constant pressure are used. This scale is sometimes called ideal gas temperature scale. At thermal equilibrium, the average kinetic energy of the translational motion of the molecules of all gases is the same. The pressure is directly proportional to the average kinetic energy of the translational motion of the molecules:. In thermal equilibrium, if the pressure of a gas of a given mass and its volume are fixed, the average kinetic energy of gas molecules must have a strictly defined value, like the temperature. to., then, or. Let us denote. The value increases with increasing temperature and does not depend on anything other than temperature. Therefore, it can be considered a natural measure of temperature. Absolute temperature scale: Let's consider the value, measured in energy units, directly proportional to the temperature, expressed in degrees:, where is the coefficient of proportionality. Coefficient ... physics and mathematics Physics... Electromagnetic phenomena ... THERMAL RADIATION. 5.3.1 Characteristics heat radiation. 5.3.2 Laws heat... and waves. MODULE 2. MOL. PHYSICS AND THERMODYNAMICS. 2.1 2.1.1 Molecular physics... 2.2 2.2.1 Thermodynamics. MODULE NO. ... 0.9c. II. THE BASES MOLECULAR PHYSICS AND THERMODYNAMICS Molecular physics and thermodynamics - sections physics, in which ... are studied, called phenomena carryover. ... thermally insulated (adiabatic) (Q = 0, A0), thermal tanks (A = 0, Q0). 2.2. Work... Mechanics. Molecular physics... Kinematics Basic concepts and ... minimal. Therefore, the entropic forces heat movements, on the contrary, tend to disorient ... as a thermometer. Phenomenon Peltier (1834) This phenomenon back phenomenon Seebeck. Energy... Designed to conduct experiments on the study of thermal phenomena, the laws of molecular kinetic theory and thermodynamic principles using digital temperature sensors. The kit allows you to carry out 13 demonstration experiments, including: Composition: 1. Digital temperature sensors -20 .. + 100 С –2 pcs. The digital sensors included in the kit are compatible with the universal demonstration measuring device. * Attention! The product image may differ from the product you received. The manufacturer reserves the right to change the configuration and specifications teaching aids without prior notice, while the functional and quality indicators of visual aids do not deteriorate.
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Thermal phenomena occur inside bodies and are entirely determined by the motion of these particles. The movement of atoms and molecules bears little resemblance to the movement of a dog or a car. The atoms and molecules of matter are in a disorderly motion, in which it is difficult to see traces of any order and regularity. The disordered movement of molecules is called thermal motion.Molecular physics. Thermal phenomena
... According to Newton's second law, the change in the momentum of a body per unit time is equal to the force acting on it:
- the basic equation of the MKT.
, in honor of the Austrian physicist L. Boltzmann is called Boltzmann constant. and properties of macrosystems were introduced by German physicist R. Clausius (1822-1888), English physicist-theorist ... that nature thermal phenomena explained in physics in two ways: thermodynamic approach and molecularly-kinetic theory of matter ...Physics... Electromagnetic phenomena(electrodynamics)
Study Guide >> PhysicsMechanics, molecular physics and thermodynamics
Study Guide >> PhysicsMechanics. Molecular physics
Abstract >> Physics
3. Heat of combustion of fuel
5. Convection in gas
6. Heat transfer between layers of liquid
7. Heat transfer due to radiation
9. Work of friction force
10. Change in internal energy during body deformation
2. Digital temperature sensor 0 ... 1000 С (has 3 measurement ranges)
3. The glass is heat-resistant
4. Tubes with stoppers
5.and other equipment for conducting physics experiments
6. Plastic storage tray with transparent lid
7. Disk with software for experimentsFor work you need:
Information about the product is for reference only and is not a public offer defined by Article 437 of the Civil Code of the Russian Federation.
