spontaneous processes自发过程

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1、SpontaneousProcesses•Aspontaneousprocessisonethatdoesoccurunderthegivensetofconditions.•Ifareactiondoesnotoccurunderagivensetofconditions,itissaidtobenon-spontaneous.SpontaneousProcessesSometypesofspontaneousprocesses:Phasetransitions(melting,freezing)Mixinganddissol

2、vingofsolutesintosolutionExpansionofgasesintoanevacuatedbulbHeattransferfromhottocoldobjectsMovementtowardschemicalequilibriumEverydayExamples:•Waterfreezesspontaneouslybelow0oCandmeltsspontaneouslyabove0oC@1atm•Alumpofsugarspontaneouslydissolvesinacupofcoffee,butdis

3、solvedsugardoesnotspontaneouslyreappearinitsoriginalform•Expansionofagasinanevacuatedbulbisaspontaneousprocess.Thegatheringofallgasmoleculesintoonelocationisnotspontaneous•Heatflowfromahotterobjecttoacolderoneisspontaneous,butthereverseneverhappensspontaneously•Irone

4、xposedtowaterandoxygenformsrust,butrustdoesnotspontaneouslychangetoironSpontaneousProcessWhatmakesaprocessspontaneous?•Often,butnotalways,asystemthatisspontaneoustriestominimizeitsenergy.•AspontaneoussystemalwaysmaximizesitsENTROPY.Entropy(S)•Entropy(S)isadirectmeasu

5、reoftherandomnessordisorderofasystem•Atdisorderincreases,Entropyincreases•EntropycanalsoberelatedtoprobabilityOrderofEntropy(S)•Forallsubstances,theparticlesinthesolidstatearemoreorderedthanthoseintheliquidstate,whicharebothmoreorderedthanthoseinthegaseousstate.Ssoli

6、d0)Entropy

7、asastatefunction•Likeenergyandenthalpy,entropyisastatefunction.∆S=Sf–Si•Ifthechangeresultsinanincreaseinrandomness,thenSf>Si•Statefunctionsarepropertiesthataredeterminedbythestateofthesystem.SecondLawofThermodynamics•Theentropyoftheuniverseincreasesinaspontaneousproc

8、essandremainsunchangedinandequilibriumprocess.Spontaneous:∆Suniv=∆Ssys+∆Ssurr>0Equilibrium:∆Suniv=∆Ssys+∆Ssurr=0EntropyChangesinthe