Entropy-and-Free-Energy熵与自由能-课件

EntropyandFreeEnergySpontaneousvs.non-spontaneousthermodynamicsvs.kineticsentropy=randomness(So)Gibbsfreeenergy(Go)

Goforreactions-predictingspontaneousdirection

thermodynamicsofcoupledreactions

GrxnversusGorxn

predictingequilibriumconstantsfromGorxn

1EntropyandFreeEnergySpontaEntropyandFreeEnergyHowcanwepredictifareactioncanoccur,givenenoughtime?Note:ThermodynamicsDOESNOTsayhowquickly(orslowly)areactionwilloccur.Topredictifareactioncanoccuratareasonablerate,oneneedstoconsider:Someprocessesarespontaneous;othersneveroccur.WHY?THERMODYNAMICSKINETICS2EntropyandFreeEnergyHowcanProduct-FavoredReactionse.g.thermitereactionFe2O3(s)+2Al(s) 2Fe(s)+Al2O3(s)DH=-848kJIngeneral,product-favoredreactionsareexothermic.3Product-FavoredReactionse.g.Non-exothermicspontaneousreactionsButmanyspontaneousreactionsorprocessesareendothermic...NH4NO3(s)+heatNH4+(aq)+NO3-(aq)

Hsol=+25.7kJ/molorhaveH=0...4Non-exothermicspontaneousreaPROBABILITY-predictorofmoststablestateWHYDOPROCESSESwithH=0occur?Considerexpansionofgasestoequalpressure:Thisisspontaneousbecausethefinalstate,withequal#moleculesineachflask,ismuchmoreprobablethantheinitialstate,withallmoleculesinflask1,noneinflask2SYSTEMCHANGEStostateofHIGHERPROBABILITYForentropy-drivenreactions-themoreRANDOMstate.5PROBABILITY-predictorofmosGasexpansion-spontaneityfromgreaterprobabilityConsiderdistributionof4moleculesin2flasksP1<P2P1>P2P1=P2Withmoremolecules(>1020)P1=P2ismostprobablebyfar6Gasexpansion-spontaneityfrDirectionalityofReactionsHowprobableisitthatreactantmoleculeswillreact?PROBABILITYsuggeststhataproduct-favoredreactionwillresultinthedispersalofenergy

or

dispersalofmatter

orboth.7DirectionalityofReactionsHowSpontaneousProcessesAprocessthatisspontaneousinonedirectionisnotspontaneousintheoppositedirection.Thedirectionofaspontaneousprocesscandependontemperature:IceturningtowaterisspontaneousatT>0C,WaterturningtoiceisspontaneousatT<0C.8SpontaneousProcessesAprocessStandardEntropies,SoEverysubstanceatagiventemperatureandinaspecificphasehasawell-definedEntropyAt298otheentropyofasubstanceiscalled

So-withUNITSofJ.K-1.mol-1ThelargerthevalueofSo,thegreaterthedegreeofdisorderorrandomnesse.g.So(inJK-1mol-1): Br2(liq)=152.2 Br2(gas)=245.5Foranyprocess:

So=So(final)-So(initial)So(vap.,Br2)=(245.5-152.2)=93.3JK-1mol-19StandardEntropies,SoEverysS(gases)>>S(liquids)>S(solids) So(J/K•mol)H2O(g) 188.8H2O(l) 69.9H2O(s)47.9IceWaterVapourEntropyandPhase10S(gases)>>S(liquids)>Theentropyofasubstanceincreaseswithtemperature.Molecularmotionsdifferenttemps.EntropyandTemperatureHigherTmeans:morerandomnesslargerS11TheentropyofasubstanceincEntropyandcomplexityIncreaseinmolecularcomplexitygenerallyleadstoincreaseinS. So(J/K•mol)CH4 248.2C2H6 336.1C3H8 419.412EntropyandcomplexityIncreaseIonicSolids:Entropydependsonextentofmotionofions.Thisdependsonthestrengthofcoulombicattraction.EntropyofIonicSubstancesEntropyincreaseswhenapureliquidorsoliddissolvesinasolvent.NH4NO3(s)NH4+(aq)+NO3-(aq)Ssol= ionpairs So(J/K•mol)MgO Mg2+/O2- 26.9NaF Na+/F- 51.5So(aq.ions)-So(s) =259.8-151.1 =108.7JK-1mol-113IonicSolids:EntropydependsEntropyChangesforPhaseChangesForaphasechange, DS=q/Twhereq=heattransferredinphasechangeForH2O(liq)--->H2O(g)DH=q=+40,700J/mol14EntropyChangesforPhaseChanTheMolecularInterpretationofEntropy15TheMolecularInterpretationoConsider2H2(g)+O2(g)2H2O(l)DSo=2So(H2O)-[2So(H2)+So(O2)]DSo=2mol(69.9J/K•mol)- [2mol(130.7J/K•mol)+1mol(205.3J/K•mol)]DSo=-326.9J/KNotethatthereisadecreaseinS

because3molofgasgive2molofliquid.CalculatingSforaReactionDSo=SSo(products)-SSo(reactants)IfSDECREASES,

whyisthisaSPONTANEOUSREACTION??

16Consider2H2(g)+O2(g)2HTheMolecularInterpretationofEntropyEnergyisrequiredtogetamoleculetotranslate,vibrateorrotate.Themoreenergystoredintranslation,vibrationandrotation,thegreaterthedegreesoffreedomandthehighertheentropy.Inaperfectcrystalat0Kthereisnotranslation,rotationorvibrationofmolecules.Therefore,thisisastateofperfectorder.ThirdLawofThermodynamics:theentropyofaperfectcrystalat0Kiszero.Entropychangesdramaticallyataphasechange.17TheMolecularInterpretationoE=q+wTheLawsofThermodynamics0.TwobodiesinthermalequilibriumareatsameT1.Energycanneverbecreatedordestroyed.2.ThetotalentropyoftheUNIVERSE(=systemplussurroundings)MUSTINCREASEineveryspontaneousprocess.STOTAL=Ssystem+Ssurroundings>03.Theentropy(S)ofapure,perfectlycrystallinecompoundatT=0KisZERO.(nodisorder)ST=0=0(perfectxll)18E=q+wTheLawsofThermo2ndLawofThermodynamicsAreactionisspontaneous(product-favored)ifDSfortheuniverseispositive.DSuniverse=DSsystem+DSsurroundingsDSuniverse>0forproduct-favoredprocessFirst,calc.entropycreatedbymatterdispersal(DSsystem)Next,calc.entropycreatedbyenergydispersal(DSsurround)192ndLawofThermodynamicsAreaConsider2H2(g)+O2(g)--->2H2O(l)DSo=2So(H2O)-[2So(H2)+So(O2)]DSo=2mol(69.9J/K•mol)- [2mol(130.7J/K•mol)+ 1mol(205.3J/K•mol)]DSo=-326.9J/KNotethatthereisadecreaseinSbecause3molofgasgive2molofliquid.CalculatingDSforaReactionDSo=So(products)-So(reactants)20Consider2H2(g)+O2(g)--->2H2(g)+O2(g)--->2H2O(l)DSosystem=-326.9J/K

2ndLawofThermodynamics212H2(g)+O2(g)--->2H2O(l)22H2(g)+O2(g)--->2H2O(liq)DSosystem=-326.9J/K

2ndLawofThermodynamics222H2(g)+O2(g)--->2H2O(liq2H2(g)+O2(g)--->2H2O(liq)DSosystem=-326.9J/KCancalc.thatDHorxn=DHosystem=-571.7kJ

2ndLawofThermodynamics232H2(g)+O2(g)--->2H2O(liq2H2(g)+O2(g)--->2H2O(liq)DSosystem=-326.9J/KCancalc.thatDHorxn=DHosystem=-571.7kJ

2ndLawofThermodynamics242H2(g)+O2(g)--->2H2O(liq2H2(g)+O2(g)--->2H2O(liq)DSosystem=-326.9J/KCancalc.thatDHorxn=DHosystem=-571.7kJDSosurroundings=+1917J/K

2ndLawofThermodynamics252H2(g)+O2(g)--->2H2O(liq2H2(g)+O2(g)--->2H2O(l)DSosystem=-326.9J/KDSosurroundings=+1917J/KDSouniverse=+1590.J/KTheentropyoftheuniverseisincreasing,sothereactionisproduct-favored.2ndLawofThermodynamics262H2(g)+O2(g)--->2H2O(l)22H2(g)+O2(g)--->2H2O(liq)DSosystem=-326.9J/KDSosurroundings=+1917J/KDSouniverse=+1590.J/KTheentropyoftheuniverseisincreasing,sothereactionisproduct-favored.

2ndLawofThermodynamics272H2(g)+O2(g)--->2H2O(liqGibbsFreeEnergy,GDSuniv=DSsurr+DSsysGibbsFreeEnergy,GDSuniv=DGibbsFreeEnergy,GDSuniv=DSsurr+DSsysGibbsFreeEnergy,GDSuniv=DGibbsFreeEnergy,GDSuniv=DSsurr+DSsysMultiplythroughby-TGibbsFreeEnergy,GDSuniv=DGibbsFreeEnergy,GDSuniv=DSsurr+DSsysMultiplythroughby-T-TDSuniv=DHsys-TDSsysDSuniv

=

-DHsysT

+

DSsys

GibbsFreeEnergy,GDSuniv=GibbsFreeEnergy,GDSuniv=DSsurr+DSsysMultiplythroughby-T-TDSuniv=DHsys-TDSsys-TDSuniv=changeinGibbsfreeenergyfortheuniverse=DGsystemGibbsFreeEnergy,GDSuniv=GibbsFreeEnergy,GDSuniv=DSsurr+DSsysMultiplythroughby-T-TDSuniv=DHsys-TDSsys-TDSuniv=changeinGibbsfreeenergyfortheuniverse=DGuniv=DGsystemUnderstandardconditions—DGo=DHo-TDSoDSuniv

=

-DHsysT

+

DSsys

GibbsFreeEnergy,GDSuniv=DGibbsFreeEnergy,GDGo=DHo-T

DSoGibbsfreeenergychange=DGo=totalenergychangeforsystem -energylostindisorderingthesystemIfreactionisexothermic(DHo<0)andentropyincreases(DSo>0),thenDGo<0,thatis,negativeandreactionproduct-favored.Ifreactionisendothermic(DHo>0),andentropydecreases(DSo<0),thenDGo>0andreactionisreactant-favored.GibbsFreeEnergy,GDGo=DHoGibbsFreeEnergy,G

DGo=DHo-TDSoDHo

DSo

DGoReactionexo(-) increase(+) - Prod-favoredendo(+) decrease(-) + React-favoredexo(-) decrease(-) ? Tdependentendo(+) increase(+) ? TdependentGibbsFreeEnergy,G DGoMethodsofcalculatingGTwomethodsofcalculatingDGoGorxn=S

Gfo(products)-S

Gfo(reactants)DetermineDHorxnandDSorxnanduseGibbsequation.b)Usetabulatedvaluesoffreeenergiesofformation,DGfo.DGo=DHo-TDSo36MethodsofcalculatingGTwomExampleAtwhatTisthefollowingreactionspontaneous?Br2(l)Br2(g)whereDH°=30.91kJ/mol,DS°=93.2J/mol.KAns:DG°=DH°-TDS°37ExampleAtwhatTisthefollowTry298Kjusttosee:DG°=DH°-TDS°DG°=30.91kJ/mol-(298K)(93.2J/mol.K)DG°=(30.91-27.78)kJ/mol=3.13kJ/mol>0Notspontaneousat298KBr2(l)Br2(g)whereDH°=30.91kJ/mol,DS°=93.2J/mol.K38Try298Kjusttosee:DG°=DHExample(cont.)AtwhatTthen?DG°=DH°-TDS°T=DH°/DS°T=(30.91kJ/mol)/(93.2J/mol.K)=0T=331.65K=58.5oC39Example(cont.)AtwhatTthen?CalculatingDG°Inourpreviousexample,weneededtodetermineDH°rxnandDS°rxntodetermineDG°rxnNow,DGisastatefunction;therefore,wecanuseknownDG°todetermineDG°rxnusing:40CalculatingDG°InourpreviousStandardDGofFormation:DGf°LikeDHf°andS°,DGf°isdefinedasthe“changeinfreeenergythataccompaniestheformationof1moleofthatsubstanceforitsconstituentelementswithallreactantsandproductsintheirstandardstate.”LikeDHf°,DGf°=0foranelementinitsstandardstate:Example:DGf°(O2(g))=041StandardDGofFormation:DGfExampleDeterminetheDG°rxnforthefollowing:C2H4(g)+H2O(l)C2H5OH(l)TabulatedDG°ffromtableslikeAppendixD:

DG°f(C2H5OH(l))=-175kJ/mol

DG°f(C2H4(g))=68kJ/mol

DG°f(H2O(l))=-237kJ/mol42ExampleDeterminetheDG°rxnfoExample(cont.)Usingthesevalues:C2H4(g)+H2O(l)C2H5OH(l)DG°rxn=DG°f(C2H5OH(l))–[DG°f(C2H4(g))+DG°f(H2O(l))]DG°rxn=-175kJ–[68kJ+(-237kJ)]DG°rxn=-6kJ<0;therefore,spontaneous43Example(cont.)UsingthesevalMoreDG°CalculationsSimilartoDH°,onecanusetheDG°forvariousreactionstodetermineDG°forthereactionofinterest(a“Hess’Law”forDG°)Example:C(s,diamond)+O2(g)CO2(g)DG°=-397kJC(s,graphite)+O2(g)CO2(g)DG°=-394kJ44MoreDG°CalculationsSimilartMoreDG°Calculations(cont.)C(s,diamond)+O2(g)CO2(g)DG°=-397kJC(s,graphite)+O2(g)CO2(g)DG°=-394kJCO2(g)C(s,graphite)+O2(g)DG°=+394kJC(s,diamond)C(s,graphite)DG°=-3kJDG°rxn<0…..rxnisspontaneous45MoreDG°Calculations(cont.)CDG°rxn≠ReactionRateAlthoughDG°rxncanbeusedtopredictifareactionwillbespontaneousaswritten,itdoesnottellushowfastareactionwillproceed.Example: C(s,diamond)+O2(g)CO2(g)DG°rxn=-397kJButdiamondsareforever….<<0DG°rxn≠rate46DG°rxn≠ReactionRateAlthoughCombustionofacetyleneC2H2(g)+5/2O2(g)-->2CO2(g)+H2O(g)Useenthalpiesofformationtocalculate

DHorxn=-1238kJ<0Usestandardmolarentropiestocalculate

DSorxn=-97.4J/K=-0.0974kJ/K<0DGorxn=-1238kJ-(298K)(-0.0974J/K) =-1209kJ<0Reactionisproduct-favoredinspiteofnegativeDSorxn.Reactionis“enthalpydriven”CalculatingDGCombustionofacetyleneCalculaGoforCOUPLEDCHEMICALREACTIONSReductionofironoxidebyCOisanexampleofusingTWOreactionscoupledtoeachotherinordertodriveathermodynamicallyforbiddenreaction:Fe2O3(s)4Fe(s)+3/2O2(g)DGorxn=+742kJ

3/2C(s)+3/2O2(g)3/2CO2(g)

DGorxn=-592kJwithathermodynamicallyallowedreaction:Overall:Fe2O3(s)+3/2C(s)2Fe(s)+3/2CO2(g)DGorxn=+301kJ25oCBUT

DGorxn<0kJforT>563oCSeeKotz,pp933-935foranalysisofthethermitereaction48GoforCOUPLEDCHEMICALREACTOtherexamplesofcoupledreactions:CoppersmeltingCu2S(s)2Cu(s)+S(s)DGorxn=+86.2kJ (FORBIDDEN)

Couplethiswith:S(s)+O2(g)SO2(s)DGorxn=-300.1kJ

Overall:Cu2S(s)+O2(g)2Cu(s)+SO2(s)

DGorxn=+86.2kJ+-300.1kJ=-213.9kJ(ALLOWED)CoupledreactionsVERYCOMMONinBiochemistry:e.g. allbio-synthesisdrivenby ATPADPforwhich

DHorxn=-20kJ

DSorxn=+34J/K

DGorxn=-30kJ37oC49OtherexamplesofcoupledreacTheConcentration

DependenceofSpontaneityAswithH°andS°,G°valueshavebeentabulatedforthestandardstateveryfewreactionsoccuratstandardconditionsnotingthatHandSchangeverylittlewithchangingT,wecanmaketheassumption50TheConcentration

DependenceTheConcentration

DependenceofSpontaneityThisworksforchangesinT,butGwillchangesignificantlywithchangingconcentrationand/orpressureForanyreactionaA+bBcC+dD51TheConcentration

Dependence5252TheConcentration

DependenceofSpontaneityOnepossiblesourceofacidrainisthereactionbetweenNO2,apollutantfromautomobileexhausts,andwater.3NO2(g)+H2O(l)2HNO3(g)+NO(g) Determinewhetherthisisthermodynamicallyfeasible(a)understandardconditionsand(b)at298K,witheachproductgaspresentatP=1.0010-6atm.Given:

G°f(NO2(g))=51.3kJ/mol

G°f(H2O(l))=-237.1kJ/mol

G°f(HNO3(g))=-73.5kJ/mol

G°f(NO(g))=87.6kJ/mol53TheConcentration

Dependence5454TheTemperature

DependenceofSpontaneityG=H-TS55TheTemperature

DependenceofBioenergeticsThebasicprocessesoflifecanbethoughtofasmakingorderoutofdisorderThisseemstogoagainstthesecondlawTocreateorder,systemsmustreleaseheattothesurroundingsLivingsystemsuselargeamountsofenergytosurvivemostcommonenergysourcesarecarbohydratesandfats56BioenergeticsThebasicprocessBioenergeticsThereactionofglucosewithoxygenishighlyspontaneousC6H12O6+6O2

6CO2+6H2OG°=-2870kJ/mol

asistheoxidationofpalmiticacidC15H31COOH+23O216CO2+16H2OG°=-9790kJ/mol57BioenergeticsThereactionofgBioenergeticsThesereactionsreleasetoomuchenergyforacelltohandlesomeoftheenergymustbestoredstoredbyconvertingADPtoATP:ADP+H3PO4ATP+H2OG°=30.6kJ/mol58BioenergeticsThesereactionsrBioenergeticsCellsuseenergystoredinATPtodrivenonspontaneousreactionsATP+H2OADP+H3PO4G°=-30.6kJ/molATPconversioncanbecoupledtootherreactionstransfersenergyfromonereactiontoanotherAminoAcidsynthesis59BioenergeticsCellsuseenergyBioenergeticsglutamicacid+NH3glutamine+H2OG°=14+kJ/molATP+H2OADP+H3PO4G°=-30.6kJ/molglutamicacid+NH3+ATPglutamine+ADP+H3PO4G°=-16.6kJ/mol60Bioenergeticsglutamicacid+NBioenergeticsCellsarenot100%efficientinstoringenergyasATP1glucosemoleculeproduces36ATPmoleculesC6H12O6+6O26CO2+6H2OG°=-2870kJ/mol36ADP+36H3PO436ATP+36H2OG°=1102kJ/molC6H12O6+6O2+36ADP+36H3PO46CO2+6H2O+36ATP+36H2OG°=-1768kJ/mol38%ATP,62%asHEAT61BioenergeticsCellsarenot100Extraslides62Extraslides62ThermodynamicsandKeqKeqisrelatedtoreactionfavorability.IfDGorxn<0,reactionisproduct-favored.

DGorxnisthechangeinfreeenergyasreactantsconvertcompletelytoproducts.Butsystemsoftenreachastateofequilibriuminwhichreactantshavenotconvertedcompletelytoproducts.Howtodescribethermodynamically?63ThermodynamicsandKeqKeqisrGrxnversusGorxn

Underanyconditionofareactingsystem,wecandefineGrxnintermsoftheREACTIONQUOTIENT,QGrxn=

Gorxn+RTlnQAtequilibrium,Grxn=0.Also,Q=K.ThusIfGrxn<0thenreactionproceedstorightIfGrxn>0thenreactionproceedstoleftDGorxn=-RTlnK64GrxnversusGorxnUnderany2NO2

N2O4

DGorxn=-4.8kJpureNO2hasDGrxn<0.ReactionproceedsuntilDGrxn=0-theminimuminG(reaction)-seegraph.Atthispoint,bothN2O4andNO2arepresent,withmoreN2O4.Thisisaproduct-favoredreaction.ThermodynamicsandKeq(2)652NO2N2O4ThermodynamicsanN2O4

2NO2

DGorxn=+4.8kJpureN2O4hasDGrxn<0.ReactionproceedsuntilDGrxn=0-theminimuminG(reaction)-seegraph.Atthispoint,bothN2O4andNO2arepresent,withmoreNO2.Thisisareactant-favoredreaction.ThermodynamicsandKeq(3)66N2O42NO2 DGorxn=+4.8ThermodynamicsandKeq(4)KeqisrelatedtoreactionfavorabilityandsotoDGorxn.ThelargerthevalueofDGorxnthelargerthevalueofK.DGorxn=-RTlnKwhereR=8.31J/K•mol67ThermodynamicsandKeq(4)KeqCalculateKforthereactionN2O42NO2

DGorxn=+4.8kJDGorxn=+4800J=-(8.31J/K)(298K)lnKDGorxn=-RTlnKThermodynamicsandKeq(5)WhenGorxn>0,thenK<1-reactantfavouredWhenGorxn<0,thenK>1-productfavouredK=0.1468CalculateKforthereactionDGEntropyandFreeEnergy

Spontaneousvs.non-spontaneousthermodynamicsvs.kineticsentropy=randomness(So)Gibbsfreeenergy(Go)

Goforreactions-predictingspontaneousdirection

thermodynamicsofcoupledreactions

GrxnversusGorxn

predictingequilibriumconstantsfromGorxn

69EntropyandFreeEnergy

SponEntropyandFreeEnergySpontaneousvs.non-spontaneousthermodynamicsvs.kineticsentropy=randomness(So)Gibbsfreeenergy(Go)

Goforreactions-predictingspontaneousdirection

thermodynamicsofcoupledreactions

GrxnversusGorxn

predictingequilibriumconstantsfromGorxn

70EntropyandFreeEnergySpontaEntropyandFreeEnergyHowcanwepredictifareactioncanoccur,givenenoughtime?Note:ThermodynamicsDOESNOTsayhowquickly(orslowly)areactionwilloccur.Topredictifareactioncanoccuratareasonablerate,oneneedstoconsider:Someprocessesarespontaneous;othersneveroccur.WHY?THERMODYNAMICSKINETICS71EntropyandFreeEnergyHowcanProduct-FavoredReactionse.g.thermitereactionFe2O3(s)+2Al(s) 2Fe(s)+Al2O3(s)DH=-848kJIngeneral,product-favoredreactionsareexothermic.72Product-FavoredReactionse.g.Non-exothermicspontaneousreactionsButmanyspontaneousreactionsorprocessesareendothermic...NH4NO3(s)+heatNH4+(aq)+NO3-(aq)

Hsol=+25.7kJ/molorhaveH=0...73Non-exothermicspontaneousreaPROBABILITY-predictorofmoststablestateWHYDOPROCESSESwithH=0occur?Considerexpansionofgasestoequalpressure:Thisisspontaneousbecausethefinalstate,withequal#moleculesineachflask,ismuchmoreprobablethantheinitialstate,withallmoleculesinflask1,noneinflask2SYSTEMCHANGEStostateofHIGHERPROBABILITYForentropy-drivenreactions-themoreRANDOMstate.74PROBABILITY-predictorofmosGasexpansion-spontaneityfromgreaterprobabilityConsiderdistributionof4moleculesin2flasksP1<P2P1>P2P1=P2Withmoremolecules(>1020)P1=P2ismostprobablebyfar75Gasexpansion-spontaneityfrDirectionalityofReactionsHowprobableisitthatreactantmoleculeswillreact?PROBABILITYsuggeststhataproduct-favoredreactionwillresultinthedispersalofenergy

or

dispersalofmatter

orboth.76DirectionalityofReactionsHowSpontaneousProcessesAprocessthatisspontaneousinonedirectionisnotspontaneousintheoppositedirection.Thedirectionofaspontaneousprocesscandependontemperature:IceturningtowaterisspontaneousatT>0C,WaterturningtoiceisspontaneousatT<0C.77SpontaneousProcessesAprocessStandardEntropies,SoEverysubstanceatagiventemperatureandinaspecificphasehasawell-definedEntropyAt298otheentropyofasubstanceiscalled

So-withUNITSofJ.K-1.mol-1ThelargerthevalueofSo,thegreaterthedegreeofdisorderorrandomnesse.g.So(inJK-1mol-1): Br2(liq)=152.2 Br2(gas)=245.5Foranyprocess:

So=So(final)-So(initial)So(vap.,Br2)=(245.5-152.2)=93.3JK-1mol-178StandardEntropies,SoEverysS(gases)>>S(liquids)>S(solids) So(J/K•mol)H2O(g) 188.8H2O(l) 69.9H2O(s)47.9IceWaterVapourEntropyandPhase79S(gases)>>S(liquids)>Theentropyofasubstanceincreaseswithtemperature.Molecularmotionsdifferenttemps.EntropyandTemperatureHigherTmeans:morerandomnesslargerS80TheentropyofasubstanceincEntropyandcomplexityIncreaseinmolecularcomplexitygenerallyleadstoincreaseinS. So(J/K•mol)CH4 248.2C2H6 336.1C3H8 419.481EntropyandcomplexityIncreaseIonicSolids:Entropydependsonextentofmotionofions.Thisdependsonthestrengthofcoulombicattraction.EntropyofIonicSubstancesEntropyincreaseswhenapureliquidorsoliddissolvesinasolvent.NH4NO3(s)NH4+(aq)+NO3-(aq)Ssol= ionpairs So(J/K•mol)MgO Mg2+/O2- 26.9NaF Na+/F- 51.5So(aq.ions)-So(s) =259.8-151.1 =108.7JK-1mol-182IonicSolids:EntropydependsEntropyChangesforPhaseChangesForaphasechange, DS=q/Twhereq=heattransferredinphasechangeForH2O(liq)--->H2O(g)DH=q=+40,700J/mol83EntropyChangesforPhaseChanTheMolecularInterpretationofEntropy84TheMolecularInterpretationoConsider2H2(g)+O2(g)2H2O(l)DSo=2So(H2O)-[2So(H2)+So(O2)]DSo=2mol(69.9J/K•mol)- [2mol(130.7J/K•mol)+1mol(205.3J/K•mol)]DSo=-326.9J/KNotethatthereisadecreaseinS

because3molofgasgive2molofliquid.CalculatingSforaReactionDSo=SSo(products)-SSo(reactants)IfSDECREASES,

whyisthisaSPONTANEOUSREACTION??

85Consider2H2(g)+O2(g)2HTheMolecularInterpretationofEntropyEnergyisrequiredtogetamoleculetotranslate,vibrateorrotate.Themoreenergystoredintranslation,vibrationandrotation,thegreaterthedegreesoffreedomandthehighertheentropy.Inaperfectcrystalat0Kthereisnotranslation,rotationorvibrationofmolecules.Therefore,thisisastateofperfectorder.ThirdLawofThermodynamics:theentropyofaperfectcrystalat0Kiszero.Entropychangesdramaticallyataphasechange.86TheMolecularInterpretationoE=q+wTheLawsofThermodynamics0.TwobodiesinthermalequilibriumareatsameT1.Energycanneverbecreatedordestroyed.2.ThetotalentropyoftheUNIVERSE(=systemplussurroundings)MUSTINCREASEineveryspontaneousprocess.STOTAL=Ssystem+Ssurroundings>03.Theentropy(S)ofapure,perfectlycrystallinecompoundatT=0KisZERO.(nodisorder)ST=0=0(perfectxll)87E=q+wTheLawsofThermo2ndLawofThermodynamicsAreactionisspontaneous(product-favored)ifDSfortheuniverseispositive.DSuniverse=DSsystem+DSsurroundingsDSuniverse>0forproduct-favoredprocessFirst,calc.entropycreatedbymatterdispersal(DSsystem)Next,calc.entropycreatedbyenergydispersal(DSsurround)882ndLawofThermodynamicsAreaConsider2H2(g)+O2(g)--->2H2O(l)DSo=2So(H2O)-[2So(H2)+So(O2)]DSo=2mol(69.9J/K•mol)- [2mol(130.7J/K•mol)+ 1mol(205.3J/K•mol)]DSo=-326.9J/KNotethatthereisadecreaseinSbecause3molofgasgive2molofliquid.CalculatingDSforaReactionDSo=So(products)-So(reactants)89Consider2H2(g)+O2(g)--->2H2(g)+O2(g)--->2H2O(l)DSosystem=-326.9J/K

2ndLawofThermodynamics902H2(g)+O2(g)--->2H2O(l)22H2(g)+O2(g)--->2H2O(liq)DSosystem=-326.9J/K

2ndLawofThermodynamics912H2(g)+O2(g)--->2H2O(liq2H2(g)+O2(g)--->2H2O(liq)DSosystem=-326.9J/KCancalc.thatDHorxn=DHosystem=-571.7kJ

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