物理化学052

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。2Answer1NH4Cl(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)=P2/223112()()1()0.2738()4PNHPHClPKPP23222()()1()0.0089()4PNHPHIPKPP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)=106.3kPa312()()0.2738()PNHPHClKP322()()0.0089()PNHPHIKP4Answer2•LetxandydenotetheamountsofHClandHIwhenthetwoequilibriumcoexistedinthereactionsystem.SotheamountofNH3inthesystemmustbex+yandthetotalamountsofthreegasis2(x+y).Thus,thepartialpressureofNH3is•and•3()()/22()totaltotalxyPNHPPxy()2()totalxPHClPxy()2()totalyPHIPxy5(wecanseethepartialpressureofP(NH3)=P(HCl)+P(HI))X=30.83yP(total)=106.3kPa12(/2)2()0.2738()totaltotalxPPxyKP22(/2)2()0.0089()totaltotalyPPxyKP6Keyprobleminthisexample•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）•7Review•1Thecriterionofaspontaneouschemical•reaction•2Thedescriptionofanequilibriumof•reaction•3Theisothermal(constanttemperature)•equation8Review1Severalsymbols[1]TheGibbsenergyofareactionsystem,G[2]ThereactionGibbsenergy:rGm=(∂G/∂)P,T[3]ThestandardreactionGibbsEnergy[4]istheGibbsenergyofmixingAandB[5]StandardGibbsenergyofformationrmGmixGfmG92Severalrelations:[1]relationofreactionGibbsenergy(rGm)tothechemicalpotentialsofthespecies,•rGm=products-reactants[2]Thestandardequilibriumconstant(K)andthestandardreactionGibbsenergy•=-RTInKo[3]generalexpressionforrGmatanarbitrarystageofthereaction,•rGm=+RTInQrmGrmG10Review[5]thermodynamicequilibriumconstant,(热力学平衡常数)canexpressedintermsofactivities(orfugacities):••KforPerfectgasreaction,solutionreactionandheterogeneousreactionhasdifferentform.[6]intermsofstandardGibbsenergiesofformation,tanoormfmfmproductsreactsGvGvG()JvJequilibriumJKarmG11Thecontentforthisclass1ThestandardGibbsenergyofreactioninsolution2Theresponseofequilibriatotheconditions•[1]Howequilibriarespondtopressure?•[2]Theeffectofinertgasonequilibria•[3]LeChatelier'sprinciple•[4]Theresponseofequilibriatotemperature•(van'tHoffequation)3Thecoexistequilibrium121ThestandardGibbsenergyofreactioninsolution•(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.rmifmiGvGrmG13•Thestandardstateforthespeciesinsolutionreactionmaybenotthepurestate.•(1)Thesolutionneednotdistinguish•solvent(溶剂)andsolute(溶质)•Equation(1)canbeusedtocalculatethe•(2)Thesolventandsoluteneeddistinguish•andthesolutionisdilute(稀溶液).•Thestandardstateofeachreactantandproductisci=1mol.dm-3andthesolutionsubmitHenry’slawhypothetical.rmG14Example•Calculatetheionizationconstant（电离常数）forbenzoicacidC6H5COOHinsolutionat298K.C6H5COOH(aq.)=C6H5COO-(aq.)+H+(aq.)•GiventhatforC6H5COOHinthesolidstate,and•forC6H5COO-(C=1.0mol.dm-3).ThesolubilityofC6H5COOHinwateris0.02787mol.dm-3at298K.1(298)245.27.fmKGkJmol1(298)223.84.fmKGkJmol152Theresponseofequilibriatotheconditions[1]Howequilibriarespondtopressure(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）()0TKP1/21()14/PK16•LeChatelier‘sprinciple:•Asystematequilibrium,whensubjectedtoadisturbance,respondsinawaythattendstominimizetheeffectofthedisturbance.•Theprincipleimpliesthatifasystematequilibriumiscompressed,thenthereactionwilladjustsoastominimizetheincreaseinpressure.ln()iximTvKVPPRT17[2]effectofinertgas(惰性气体)onequilibrium•1.Ifaninertgasisaddedtoanequilibriummixtureofgasesatconstanttemperatureandvolume,thereisnoeffectontheequilibrium.•Becausetheadditionofaninertgasleavesthemolarconcentrationsoftheoriginalgasesunchanged,astheycontinuetooccupythesamevolume.18•2.Ifaddinganinertgasatconstanttemperatureandpressurewhichhasthesameeffectasloweringtheoriginalgaspartialpressure.•If,theadditionofaninertgasatconstantpressurereducesthesumofthepartialpressureofthereactantsandproducts,andthereactionshiftstothelefttocompensateforthis.•(/){}()iiifgfgvvvFGFGPxdedeDEDEiinertsixxnnPKKPPPxxnnPnn0iv19Example•At1273Kandatotalpressureof30.4atmtheequilibriuminthereactionCO2(g)+C(s)=2CO(g)issuchthat17mol%ofthegasisCO2.•(a)WhatwouldbeCO2ifthetotalpressurewere20.3atm?(b)WhatwouldbetheeffectontheequilibriumofaddingN2tothereactionmixtureinaclosedvesseluntilthepartialpressureofN2is10atm?©Ifthereactant