物理化学052ppt课件

.,1,例题,例3.在一抽成真空的容器中单独放有NH4Cl(s)，在340oC时分解反应NH4Cl(s)=NH3(g)+HCl(g)的平衡压力P1=104.6kPa；同样条件下，若单独放有NH4I(s),分解反应NH4I(s)=NH3(g)+HI(g)的平衡压力P2=18.85kPa。求NH4Cl(s)与NH4I(s)两种纯固态物质同时存在，加热到340oC，当上述两个反应都达到平衡时，系统的总压为多大?设HI(g)不分解，两个盐类不形成固态溶液。,.,2,Answer1,NH4Cl(s)alone:NH4Cl(s)=NH3(g)+HCl(g)P(NH3)=P(HCl)=P1/2NH4I(s)alone:NH4I(s)=NH3(g)+HI(g)P(NH3)=P(HI)=P2/2,.,3,WhenNH4Cl(ammoniumchloride)andNH4I(ammoniumiodide)coexistinthesystem,thepartialpressure(分压)ofammonia(NH3)gasmustaccordwithbothtwoequilibriummentionedabove.IfthepartialpressureisP(NH3)forNH3(g),P(HCl)forHCl(g)andP(HI)forHI,So(1)(2)andP(NH3)=P(HCl)+P(HI)(3)TheanswerisP(total)=P(NH3)+P(HCl)+P(HI)=106.3kPa,.,4,Answer2,LetxandydenotetheamountsofHClandHIwhenthetwoequilibriumcoexistedinthereactionsystem.SotheamountofNH3inthesystemmustbex+yandthetotalamountsofthreegasis2(x+y).Thus,thepartialpressureofNH3isand,.,5,(wecanseethepartialpressureofP(NH3)=P(HCl)+P(HI)X=30.83yP(total)=106.3kPa,.,6,Keyprobleminthisexample,1.Thepartialpressureisaintensivevariable(强度变量）,andtheamountofspeciesisextensivevariable(广度变量）2.Equilibriumconstantforheterogeneousreactions(复相反应的平衡常数)3.Thecalculaterulefortheequilibriacoexistedinasystem(同时平衡的计算原则）,.,7,Review,1Thecriterionofaspontaneouschemicalreaction2Thedescriptionofanequilibriumofreaction3Theisothermal(constanttemperature)equation,.,8,Review,1Severalsymbols1TheGibbsenergyofareactionsystem,G2ThereactionGibbsenergy:rGm=(G/)P,T3ThestandardreactionGibbsEnergy4istheGibbsenergyofmixingAandB5StandardGibbsenergyofformation,.,9,2Severalrelations:1relationofreactionGibbsenergy(rGm)tothechemicalpotentialsofthespecies,rGm=products-reactants2Thestandardequilibriumconstant(K)andthestandardreactionGibbsenergy=-RTInKo3generalexpressionforrGmatanarbitrarystageofthereaction,rGm=+RTInQ,.,10,Review,5thermodynamicequilibriumconstant,(热力学平衡常数)canexpressedintermsofactivities(orfugacities):KforPerfectgasreaction,solutionreactionandheterogeneousreactionhasdifferentform.6intermsofstandardGibbsenergiesofformation,.,11,Thecontentforthisclass,1ThestandardGibbsenergyofreactioninsolution2Theresponseofequilibriatotheconditions1Howequilibriarespondtopressure?2Theeffectofinertgasonequilibria3LeChateliersprinciple4Theresponseofequilibriatotemperature(vantHoffequation)3Thecoexistequilibrium,.,12,1ThestandardGibbsenergyofreactioninsolution,(1)BecausethevalueofstandardGibbsenergyformation(标准生成吉布斯自由能)isforapurespecies,sothevalueofthestandardreactionGibbsenergy(反应的标准吉布斯自由能变)indicatedthatthestandardstateofeachreactantandproductisinthepurestate.,.,13,Thestandardstateforthespeciesinsolutionreactionmaybenotthepurestate.(1)Thesolutionneednotdistinguishsolvent(溶剂)andsolute(溶质)Equation(1)canbeusedtocalculatethe(2)Thesolventandsoluteneeddistinguishandthesolutionisdilute(稀溶液).Thestandardstateofeachreactantandproductisci=1mol.dm-3andthesolutionsubmitHenryslawhypothetical.,.,14,Example,Calculatetheionizationconstant（电离常数）forbenzoicacidC6H5COOHinsolutionat298K.C6H5COOH(aq.)=C6H5COO-(aq.)+H+(aq.)GiventhatforC6H5COOHinthesolidstate,andforC6H5COO-(C=1.0mol.dm-3).ThesolubilityofC6H5COOHinwateris0.02787mol.dm-3at298K.,.,15,2Theresponseofequilibriatotheconditions,1Howequilibriarespondtopressure(P234):Thestandardequilibriumconstantisindependentofthepressure,buttheequilibriumcompositiondependsonthepressure.(压力对化学平衡的影响，实际上并非是对平衡常数的影响，而是指对平衡移动的影响）,.,16,LeChateliersprinciple:Asystematequilibrium,whensubjectedtoadisturbance,respondsinawaythattendstominimizetheeffectofthedisturbance.Theprincipleimpliesthatifasystematequilibriumiscompressed,thenthereactionwilladjustsoastominimizetheincreaseinpressure.,.,17,2effectofinertgas(惰性气体)onequilibrium,1.Ifaninertgasisaddedtoanequilibriummixtureofgasesatconstanttemperatureandvolume,thereisnoeffectontheequilibrium.Becausetheadditionofaninertgasleavesthemolarconcentrationsoftheoriginalgasesunchanged,astheycontinuetooccupythesamevolume.,.,18,2.Ifaddinganinertgasatconstanttemperatureandpressurewhichhasthesameeffectasloweringtheoriginalgaspartialpressure.If,theadditionofaninertgasatconstantpressurereducesthesumofthepartialpressureofthereactantsandproducts,andthereactionshiftstothelefttocompensateforthis.,.,19,Example,At1273Kandatotalpressureof30.4atmtheequilibriuminthereactionCO2(g)+C(s)=2CO(g)issuchthat17mol%ofthegasisCO2.(a)WhatwouldbeCO2ifthetotalpressurewere20.3atm?(b)WhatwouldbetheeffectontheequilibriumofaddingN2tothereactionmixtureinaclosedvesseluntilthepartialpressureofN2is10atm?IfthereactantgasescontainamoleofN2inadditionto1moleofCO2,whatistheequilibriumextentofreactionat30.4atm?(d)Atwhatpressureofthereactantswill25%ofthegasbeCO2?,.,20,4Theresponseofequilibriatotemperature,AccordingtoLeChateliersprinciple,asystematequilibriumwilltendtoshiftintheendothermicdirectionifthetemperatureisraised,whiletheequilibriumtendtoshiftintheexothermicdirectionifthetemperatureislowered.,.,21,ThevantHoffequation,ThevantHoffequationisanexpressionfortheeffectoftemperatureonthestandardequilibriumconstantKo.HereisthestandardreactionenthapyatthetemperatureT.,.,22,thevalueofKatdifferenttemperature,General,theintegral(积分)ofVantHoffEquationisusedforgasreactionwhichthepressureislow.(1)Ifvariesonlyslightlywithtemperatureoverthetemperaturerangeofinterest,theintegralofequationfromT1toT2yiels,.,23,(2)Ifdependsontemperature,Specially,whentheheatcapacities(热容）ofreactantsandproductsisthemeanvalue,thevalueofisconstant,then,.,24,3Theeffectofinitialcompositiononequilibrium,Forexample,considertheequilibr