1、Thermodynamic systems and equilibrium statesThermodynamic systems and equilibrium statesThe thermodynamic system1The difference between thermodynamics and mechanics 2Equilibrium and non-equilibrium3The thermodynamic equilibrium 41.The thermodynamic systeml There may be interactions between the syste
2、m and the outside world,such as heat transfer,work,mass exchange,etcsysteml System classificationopen systemisolated systemThere is no exchange of matter or energy between the system and the outside world.closed systemNo matter is exchanged between the system and the outside world,only energy(heat,w
3、ork)is exchanged.A system is made up of a large number of molecules,such as gases in a cylinder.There is an exchange of matter and energy between the system and the outside world.The object of thermodynamics is called the thermodynamic system2.The difference between thermodynamics and mechanics1.The
4、 attention of thermodynamics is directed inward.The research method of thermal physics differs from the macroscopic description of other disciplines such as mechanics.Differences between thermodynamics and mechanics:2.The macroscopic mechanical motion of the system as a whole is generally not consid
5、ered in thermal physics.If the system is in motion as a whole,the coordinate system is usually established on the moving object.Thermodynamic parameters:macroscopic quantities(such as pressure,volume,temperature,etc.)that are related to the internal state of the system.Example:For the oxygen cylinde
6、r on a moving truck,the coordinate system is taken in the oxygen cylinder.3.Equilibrium and non-equilibrium Definition of equilibrium state:The system will come to a state which appears to be unchanged with time on the macro level after a long enough time without being affected by external condition
7、s.This state is called equilibrium state.Macroscopic properties remain unchangedNot affected by the outside worldExplanation(1)Being unaffected by the outside world means that there is no energy or particle exchange between the system and the outside world,such as:The metal bar in ice water and boil
8、ing water at both ends is a stable state,not an equilibrium state.The particle density of a gas system in a gravitational field varies with height,but it is an equilibrium state.low temperature T2high temperature T1In the case of heat flow or particle flow,the state where the macroscopic states do n
9、ot change with time is called steady state or stationaly state-simple non-equilibrium stateThe correct discriminant method should depend on whether there is heat flow and particle flowwith no heat flow or particle flowno change with time at the macro levelequilibrium stateNote:Quasi-static processes
10、(2)Equilibrium is thermal dynamic equilibrium(3)The macroscopic quantities of an equilibrium gas system can be represented by a set of determined values(P,V,T)(4)Equilibrium is an ideal statep1(p1,V1,T1)OV2(p2,V2,T2)(5)Description of non-equilibrium state:local equilibrium.4.Thermodynamic equilibriu
11、m)1.Condition of thermal equilibrium:The temperature in the system is always the same.The heat flow is caused by the inhomogeneity of the temperature inside the system.There are two kinds of particle flow,one is the macroscopic particle flow that can detect the directional movement of groups of part
12、icles.2.Conditions of mechanical equilibrium:the mechanical equilibrium should be achieved between the internal parts of the system and between the system and the outside world.3.Condition of chemical equilibrium:the chemical composition of the parts of the system should be the same everywhere witho
13、ut outside action.The second type of particle flow does not have the macroscopic migration of particles caused by the directed motion of swarms.oxygenOxygen and nitrogen mixture nitrogenExample：diffusion Definition of equilibrium state:The system will come to a state which appears to be unchanged wi
14、th time on the macro level after a long enough time without being affected by external conditions.This state is called equilibrium state.The correct discriminant method should depend on whether there is heat flow and particle flowwith no heat flow or particle flowno change with time at the macro levelequilibrium stateThermodynamic equilibrium:mechanical equilibrium,thermal equilibrium,chemical equilibriumThanks！
