浙江大学 普通化学 化学原理 英文课件Chapter 18热力学.pptVIP

Chapter18ThermodynamicsInthisChapter,wewilladdressseveralaspectsasfollows:I)Howtopredictwhetherareactionunderagivenconditionscanoccurornot?II)Howtomakethereactionhappen,ifitdoesnotproceedunderprimaryconditions?SpontaneityandEntropy(S).TheSecondandThirdLawsofthermodynamics.FreeEnergy(G)andEquilibrium(K).

Spontaneousprocess:spontaneousnon-spontaneous18.2Goaheadbyitself,withouthelpfromsurroundings.spontaneousNon-spontaneous

Whatarethefactorscontrollingthespontaneity?CH4(g)+2O2(g)CO2(g)+2H2O(l)DH0=-890.4kJH+(aq)+OH-(aq)H2O(l)DH0=-56.2kJH2O(s)H2O(l)DH0=6.01kJNH4NO3(s)NH4+(aq)+NO3-(aq)DH0=25kJH2OEnergyFreedom

Entropy(S):ameasureofsystemdisorder.orderSdisorderSDS=Sf-SiDS0Foragivensubstance:SsolidSliquidSgasH2O(s)H2O(l)DS018.2Heatinghydrogengasfrom600Cto800CCrystallizationfromasupersaturatedsolutionDS0Foraprocess:

EntropyisalsoaStatefunction.E1H1S1E2H2S2n1P1V1T1n2P2V2T2State1State2DE=E2–E1DH=H2–H1DS=S2–S1ThevalueofSisonlydeterminedbythestate,regardlessofhowthestateisreached.

HowtoquantifytheEntropy?MicrostatesW=1W=4W=6SIn1868,BoltzmannproposedS=klnWDS=Sf-SiForaprocess:DS=klnWfWiBoltzmannconstantk=1.38×10-23J/KForCH3OHandC2H5OH:SmethanolSethanol

TheSecondLawofThermodynamicsTheentropyoftheuniverseincreasesinaspontaneousprocess,andremainsunchangedinanequilibriumprocess.DSuniv=DSsys+DSsurr0(1)Spontaneousprocess:DSuniv=DSsys+DSsurr=0(2)Equilibriumprocess:Inordertopredictthedirectionofachemicalreaction,however,bothDSsysandDSsurrneedtobecalculated,whichisaquestionremainingtobesolved.

HowtocalculateDSsurr,theentropychangeinthesurroundings?EndothermicDHsys0DSsurr??DHsys