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1、2.2Thefirstlawofthermodynamics 2.2.1WorkandHeat(1)Heat:Theenergyexchangedortransferredbetweenthe system and the environment due to differenttemperature,whichisexpressedinQ.ThesystemabsorbsheatfromenvironmentandQismorehigherthanzeroTheheatreleasesfromsystemtotheenvironmentandQislessthanzeroQisrelated
2、tothespecificpathwayofchange,So,Qisnotastatefunction2.Work:Besides the heat,the other energy that istransmittedbelongstowork,whichisrepresentedbyW.Thespecifiedenvironmentworksonthesystem,Wishigherthan0Whenthesystemworksontheenvironment,Wislessthan0 Workisrelatedtopathways,so,Workisnotastatefunctiony
3、et.VolumetricworkNon-volumetricwork(suchaselectricworkandsurfacework)classificationVolumetricwork(Expansionwork)Whenthevolumeofthesystemchanges,theworkdonebythesystemagainstexternalpressureisnamedasvolumetricworkPex:ExteriorpressurevalueV：ChangevalueinvolumepexV1Whencalculatingthevolumetricworkofide
4、algasintheisobaricprocess,itshouldbenotedthattheinitialandfinalpressuressizeofthesystemarethesame,whichequaltotheenvironmentalpressurevalue.p1 p2 pe constantW pe S l pe Vp VF pe SVolumetricworkillustrationsHeatandworkarephysicalquantitiesassociated with processes.There is no heat orwork until the sy
5、stem changes,so neither heatnorworkisastatefunction.Whendealingwithheatandwork,wemustconsidernotonlytheprocess,butalsotheapproach.HeatandWorkdontbelongtostatefunctions2.2.2thermodynamicenergyIt refers to the sum of the energy of thematerialsinsidethesystem,includingtranslationalenergy,rotational ene
6、rgy,vibrational energy,electronic energy,nuclear energy of molecularmotion,potential energy of interaction amongvariousparticles,etc.Itbelongstoastatefunction,andisexpressedbysymbolU.Itsabsolutevaluecantbeknown,butchangevaluecouldbemeasured.Theinternalenergyofthermodynamics(U)：whichreferstothesumofa
7、llkindsofenergyof molecular movements,including the totalenergyofallmicroparticlesinthesystem.U belongs to a state functionwhichisonlyrelatedtotheinitialandfinalstates,butnothingtodowiththepathwayofchange.2.2.3thefirstlawofthermodynamicsLaw of conservation and transformation of energy In1850,thescie
8、ntificallyrecognizedlawofconservation of energy is one of the universallawsofnature.Whichpresentthatallmaterialsinnaturehaveenergyinthepresenceofvariousforms.Itcan be transferred from one type to another.Thetotalamountofenergyremainsthesameintheprocessofconversion.Professionaldemonstration:TheFirstL
9、awofThermodynamicsis the special form of the conservation andtransformationofenergyinthefieldofthermalphenomena,indicating that the internal energy,heat and work of thermodynamics can betransformed into each other,while the totalenergyremainsthesame.Inotherwords,thefirstlawofthermodynamicscanalsobee
10、xpressedthatthefirstkindofperpetualmotionmachineisimpossibletobemade,derivingfromsummaryofhumanexperiences.Firstkindofperpetualmotionmachine:isthatakindofmachineneitherrelyontheoutsidetoprovideenergy,norreduceenergyitself,butcancontinuously do external work.It obviouslycontradictsthelawofconservatio
11、nofenergy.Inhistory,therewasapassionformakingthiskindofmachine.Butitallendsinfailure.Q、WState(I)State(II)U1 U2 U2=U1+Q+W U=U2 U1=Q+WAmathematicalexpressionofthefirstlawofthermodynamicsforaclosedsystemThefirstlawofthermodynamics:The transformation of energy canoccurvisdifferenttypes,butintheprocessof
12、transformation,thetotalvalueofenergyisalwaysthesame.Theessenceofthefirstlawofthermodynamicsisthelawofconservationandtransformationofenergy.AsforthesignofQandW：Qishigherthanzerowhenthesystemabsorbsheatfromtheenvironment,andviceversa,Qislessthanzerowhenthesystemreleasesheattotheenvironment.Wishigherth
13、an0whentheenvironmentworksonthesystem,andviceversa,Wislessthan0whenthesystemworksontheenvironment.Example 1:For a closed system,50 kilojoules of absorbed heat took place from environment during a certain process,meanwhile,30 kilojoules of Work works on environment.How much is the changed value of internal energy of thermodynamics in the whole process of this system?Usystem=(+50kJ)+(-30kJ)=20kJTheinternalenergyofthermodynamicsincreasedby20kJ.Question:Uenvironment=？TheIsolatedsystem:Q=0，W=0，U=0Thecirculatorysystem:U=0Q=-W
