热学课件 ppt.ppt

1、1,Thermal physics,instructor：葛大勇,热 学,Bilingual education：,2,教材及教学参考书: 1、 热学，秦允豪，高等教育出版社，2004年 第 二版； 2、 热学，李椿 章立源 钱尚武，高等教育出版社， 1979年第一版； 3、热学，赵凯华 罗蔚茵，高等教育出版社，1998 第一版； 4、Thermal Physics,C.B.P.Finn, Routledge The second law of thermodynamics: Concerning the thermal process is irreversible. 19 centurie

2、s, the kinetic theory of gases: heat is performance that molecule sport. the kinetic theory of gases statistics mechanics ( apply to thermal radiation) quantum, development quantum mechanics at 1926.,7,伽利略温度计 16世纪 (明),从钻木取火到商周的青铜器,8,瓦特早期蒸气机,9,1807年,10,1823年,11,1892年,12,1.2 Equilibrium state of therm

3、odynamics system,1.2.1 equilibrium state For instance: suppose an airproof container is divided into two fractions A and B, there is ideal gas in A (the pressure is p0) and vacuum in B ( see graph).,13,Anther example: when two object which have different temperature contact with each other, the hot

4、one will become cold, and the cold one will become hot. Till they attain the state that there have same temperature in everywhere. At this time, if no effect from outsider, two bodies will always keep this state, no longer take place any macroscopic variety.,14,Definition to the equilibrium state: m

5、acroscopic variables have definite values that remain constant so long as the external conditions are unchanged.,Note: here the external conditions are unchanged, means the outsider to system will not do work, and do not transmit heat too.,15,1.2.2 The state variables,When the system is placed in th

6、e equilibrium state, having some attribute that can be taken by some certain physical quantity. So, we can select the variable to describe system state, call it as the state variables . Usually, four variables to be used to describe the equilibrium state of the thermodynamics system. (1) mechanics v

7、ariables: Pressure P; (2) geometric variables: Volume V, length L; (3) chemical variables: Mole number n, composition Xi; (4) electromagnetic variables: Electric field E, electric polarization P, magnetic induction B, magnetization M.,16,1.3 temperature,Use the temperature to express the cold or hot

8、 of body, but to solve every kind of thermal knowledge, this kind of cognition is still not enough, must make the thorough comprehension to the concept of temperature.,17,1.3.2 The zeroth law of thermodynamics,Such as the graph, two thermodynamics system 1,2 be placed in their equilibrium state( X,

9、Y) and( X, Y) each at first. 绝热板:adiabatic wall 导热板:conducting wall,18,A kind of special situation is after thermal contact, the states of two systems do not take place any variety, this show the two systems have come to the thermal equilibrium at the time they contact beginning. According to this f

10、act, we can also use the concept of thermal equilibrium to the system that do not take place the thermal contact. This means: if make these two systems got in touch with each other, they can attain the thermal equilibrium under the situation that their states do not take place the variety.,19,For ex

11、ample: take three thermodynamics system A, B, the C .,20,conclusion : Under no external effect, if each of two systems is in thermal equilibrium with a third, they are in thermal equilibrium with one another. This law is called thermal equilibrium law, also be called the zeroth law of thermodynamics

12、,Note: This reason is easy, but not obviously. For example, two iron can magnetize the magnet, but they are not magnetize with each other.,The physics meaning of the zeroth law of Thermodynamics:,21,1.3.3 Thermometric scale,The value representation of the temperature is called the thermometric scale

13、.,liquid thermometer: scribed the temperature with the volume of liquid. This kind of thermometer general adopt in Celsius thermometric scale. Stipulate ice point is 0 Celsius, steam point is 100 Celsius, and the change that the volume of liquid to make with the temperature is linear. Engrave the th

14、ermometer accord linear relation between 0 Celsius and 100 Celsius.,22,Creating a kind of thermometric scale demand three main factors: use a certain matters (be called thermometric matter) property which change with temperature ( be called thermometric property) to scribe temperature ; (2) select a

15、 standard fixed point; (3) define the relationship between the thermometric property and temperature.,23,The other thermometric property of matter: Mechanical: The pressure P of gas that keep the volume not change; the tension J of the rubber; geometric: The volume V of gas that keep the pressure no

16、t change, the volume V of the liquid; Electrical: Resistance R, the electromotive force of the thermocouple. According to these thermometric property of matter, can make into various thermometers, also can have various thermometric scale, this kind of thermometric scale is called the empirical therm

17、ometric scales.,24,1.3.3.1 Gas thermometer,The gas thermometer has two kinds, one is constant volume gas thermometer; the other is constant pressure gas thermometer.,Constant volume gas thermometer:,25,1.3.3.2 The ideal gas thermometric scale,Use T(P) express the temperature which the constant volum

18、e gas thermometer attains thermal equilibrium with system, and use P express the gas pressure got by thermometer, set the relation between T(P) and P is direct ratio, that is,Since 1954, international stipulate only use one standard fixed point to create thermometric scale, which is the triple point

19、 of water: means the pure ice, pure water and water steam balanced coexist, the temperature strictly is 273.16 K.,26,Use the Ptr express the pressure that at the triple point of water, we can get:,Namely:,Then:,But, only when ,the gas in B is ideal gas, so should add limit condition to the equation:

20、,27,experiment can as follows proceed: In the same measure bubble successively fill up same gas of the different mass, then find out the pressure at the triple point of water and the temperature of measurement (such as the steam point of water) at different mass of gas ,Ptr and Psteam .from equation

21、 get the temperature T( P) at different mass of gas, then draw the T( P) Ptr graph, prolong the curve ,the value of temperature for testing will be found out.,As the graph, the four curves is get from the steam point of water use four different gases according the method of experiment.,28,The thermo

22、metric scale of ideal gas do not depend on any character of gas, using different gas can get same temperature ( because all the pressure tend to zero), but after all it depend on the commonness of gas, to very low temperature (below the liquefaction point of the gas) and very high temperature (1000

23、s are the upper limits) will not can be used.,the volume V is constant:,the pressure P is constant :,29,1.3.3.3 Thermodynamics thermometric scale,Create a kind of thermometric scale, do not depend on any thermometric matter and its physics attributes, on the history Kelvin first led into the thermod

24、ynamics thermometric scale, also calling Kelvin thermometric scale. The temperature with this kind of thermometric scale being called the thermodynamics temperature, express by T, the unit calls Kelvin, express by K. By definition, 1 Kelvin is equal to 1/273.16 of the thermodynamics temperature of t

25、he triple point of water.,30,1.3.3.4 Celsius thermometric scale and Fahrenheit thermometric scale,The temperature get by Celsius thermometric scale is expressed by “t”, define it: t=T-273.15 the unit of the temperature of Celsius calls the degree of Celsius, write as .,Another thermometric scale Fah

26、renheit thermometric scale (Fahrenheit), write as , definition is:,31,1.4 The equation of state of gas,We call the corresponding relation of thermodynamics variable in thermal equilibrium state equation of state, its concrete form come from the experiment.,32,1.4.3 the equation of state of ideal gas

27、,1.4.3.1 Boyle law ( the experiment law of the gas) England scientist Boyle in 1662 and France scientist Mariotte in 1679, independent think out from experiment successively: When the temperature of the certain mass gas is constant, its pressure times volume is a constant, PV= C The constant C has d

28、ifferent value at different temperature; this relation is called the Boyle law, sometimes also being called Boyle-Mariotte law.,33,1.4.3.2 The equation of ideal gas state,First, according to Boyle law and the definition of the thermometric scale of ideal gas to certain the relation between the const

29、ant C in the equation and the temperature T . Suppose the value of constant C at the triple point of water is Ctr. Measure the temperature with the constant pressure gas thermometer, and the pressure is Ptr ,volume is Vtr at the triple point of water, the volume is V at any temperature. So according

30、 the equation ,we have:,34,Put it in the equation of definition of pressure constant gas scale,get:,so:,Then put it in equation , get:,35,Mention before, the experiment result expresses, whether use what kind of gas, regardless constant volume or constant pressure, when the pressure tend to zero, th

31、e thermometric scale have the same terminal value- thermometric scale of ideal gas T. Therefore, under the situation that the pressure tend to zero, use T replaces the above T(V), and rewrites the equation as:,36,Under certain temperature and pressure, the volume of the gas with its mass M or mole n

32、umber (, the is the mole mass of the gas) has direct ratio. If use v express the volume of one mole gas, then V=v, for Ctr=PtrVtr=Ptrvtr, Then the equation can be further written as:,37,According to the Avogadre law: when the pressure of gas tend to zero, under same temperature and pressure ,molar v

33、olume of gas is same.,Then:,The equation of state is get by use Boyle law, the definition of the thermometric scale of ideal gas and the Avogadre law . At the limit situation of pressure tend to zero, every kind of gas obey it strictly.,38,1.4.4.3 the universal gas constant R,Have known according to

34、 the experiment result: the volume of 1 mole ideal gas at 273.15K and 1 atmosphere pressure is:,So get:,If the unit of P0 uses atm, the unit of v0 uses lmol-1, then get:,39,1.4.4 The equation of the state of mixed ideal gas,Dalton disjoin pressure law: The pressure of mixed gas equal to the sum of p

35、ressure of every component. P= P1+ P2+ + Pn,40,求空气的平均摩尔质量？已知按质量百分比来说，空气中含有氮气76.9%，氧气23.1%。,解：,41,Example 1: During a chemistry laboratory experiment, a sample of hydrogen gas is collected into a 0.50-liter flask at room temperature (23 ) and pressure (1.00atm). It is cooled to 5.0 and transferred to

36、 a container whose volume is 0.12L. What pressure does the gas exert on the walls of the final container.,42,Solution: at the initial conditions, we have At the new container, we have Because the number of moles of gas is constant, we can combine the equation of state for the two situations, to get

37、or Substituting the data gives,43,例题2：混合气体是由1、2、3.n中组分的气体组成。已知它们的质量和摩尔质量分别为M1、M2和1，2.。混合气体的压强为P，求各种气体分压强的表达式。,44,解：第i种气体产生的分压强Pi应满足如下的状态方程： （1） 混合气体的总压强P，也应满足下式： （2） 式中M和分别为混合气体的质量和摩尔质量，它们之间的关系为： （3）把（1）与（2）式相除后，再利用（3）式，得：,45,例题3：半透膜将容积V=100升的容器分成相等的两部分，一部分内有质量M1=2克的氢气，另一部分内是1摩尔的氮气，如果半透膜只让氢气通过，两部分的温

38、度均是t=127，而且保持不变，求容器内两部分的压强。,46,解：因为氢气能自由通过半透膜，所以它是充满在整个容积V中，则： 式中1是氢的摩尔质量，P1是氢气充满整个容积V时产生的压强，也等于始终存在一种氢气的那部分容积中的压强 氮气的状态方程是： 因为在这一半的容器内有氢气和氮气，所以总压强P应是分压强P1和P2之和，即：,47,例题4： 一只打气筒，每打一次可将原来压强为P0=1.0大气压，温度为t0=-3.0，体积V0=4.0升的空气压缩到容器中。设容器的容积V=1.5103升，问需要打几次气，才能使容器内的空气温度为t=45，压强为P=2.0大气压。假设未打气前容器中原来就有t=45，

39、压强P0=1.0大气压的空气。,48,解：设打一次气送入容器中的空气质量为： 容器中原有的空气质量为： 容器中最后所含的空气质量为： 送入容器的空气总质量为： 因此需打入的次数为： 把P0=1.0atm，T0=273-3=270K，V0=4.0升 P=2.0atm，T=273+45=318K，V=1.5103升代入上式，得：,49,例题5： 一气缸内贮有理想气体,气体的压强、摩尔体积和温度分别为P1，v1，和T1。现将气缸加热，使气体的压强和体积同时增大。设在这过程中，气体的压强P和摩尔体积v满足下列关系式：P=Kv，其中K为常数。 （1）求常数K，将结果用P1，T1和普适气体常数R表示。 （

40、2）设T1=200K，当摩尔体积增大到2v1时，气体的温度是多高？,50,解：气缸内1摩尔气体在加热前后个状态参量应满足： （1）当气体处于P1，v1和T1的状态下，有 但又必须满足状态方程： 两式消去v1，得：,51,（2）当气体的摩尔体积v2=2v1时，则 但又必须满足下列方程： 解出： 所以：,52,1.5 the microscopic model of matter,(1) The macroscopic matter is made up by a lot of particles molecule (or atom). (2) The molecules of matter ar

41、e always moving, and this movement is ruleless, in relation with temperature of the matter. For explaining this property, introduce two kinds of phenomena: Diffusion and Brown movement. (3) There have the interaction force of molecule between molecules,If want to discuss matter from the micro view,

42、should know its microscopic structure first.,53,1.6 The microscopic model of ideal gas The experiment confirms, can make suppose to ideal gas as follows: (1) When compared with the average distance of the molecule, the size of molecule oneself can be neglected. (2) Except the time when take place co

43、llision, the interaction force of the molecule can be neglected. The molecule makes beeline movement freedom. (3) Be placed in equilibrium state of ideal gas, the bump between molecules and molecule with container is perfect elastic collision, that means the kinetic energy of gas molecule will not l

44、oss because of bump, and keep momentum and kinetic energy conservation during elastic collision.,54,1.6.3 The pressure of ideal gas,Think there have a quantitative ideal gas in a container whose shape is random, the volume is V, and have N molecules, and the number of molecule in the unit volume is

45、n= N/ V, the mass of each molecule is m, and the velocity of molecule has different directions and values. For the convenience of discussion, can divide some teams of molecules, in every team, the molecules have the velocity that is same direction and value. And suppose the number of molecules in ev

46、ery team is n1，n2nirespectively, then:,55,Under the equilibrium state, the pressure is equal at anywhere of container wall , take a part of area dA vertical to X axis, calculate the pressure it suffers.,First consider the action that a single molecule makes to dA. velocity is Vi, the three parts val

47、ue of velocity is ViX, ViY, ViZ ; Because the collision is perfect elastic, so in the direction of X the value of velocity is change from ViX to - ViX . So the change of molecule momentum during the collision process is:,the impulse that the molecule make to dA is:,56,(2) Second, confirm the total i

48、mpulse that all molecules make to dA during a period of time dt.,The number of molecules which can have collision with dA during the time dt is:,So the total impulse that the molecule whose velocity is Vi put on dA during the time dt is:,the total impulse dI that all the molecule put on dA is:,57,Th

49、e gas in the container is not move as a whole, so speak averagely, the number of molecule whose velocity is during Vix0 is equal to half of the total number of molecule, and the number of Vix0 in the process of make sum, then should divided with 2 to the equation, hence get:,And then get:,58,If use

50、to express the average value that Vx2 of all molecules, which means:,Then get:,For:,So:,express the average value of the smooth kinetic energy of gas molecule,59,1.6.4 The microscopic explanation of temperature,Get:,So:,Then:,60,If write:,Then can get:,be called the root-mean-square velocity, expres

51、sed by Vrms.,61,Example 6: On the average, how fast is a nitrogen molecule moving in air at 27?,62,Solution: for diatomic nitrogen gas, M=28.0g/mol, and so: Then:,63,the definitions equation of root-mean-square velocity is:,64,1.7 The force of molecule,1.7.1 The equation of molecular force,(st),(1)T

52、he r is the distance between centers of two molecules, and , , s, t is positive constant number which have something to do with the character of molecule; (2) The first term is positive, meaning the repulsion force; the second term is negative, meaning the attraction force; (3) The s and t is bigger, for example, to the molecule of inert gases, s=13, t=7.,65,1.7.2 The curve of molecular force