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 1Severalsymbols 1 TheGibbsenergyofareactionsystem G 2 ThereactionGibbsenergy rGm G P T 3 ThestandardreactionGibbsEnergy 4 istheGibbsenergyofmixingAandB 5 StandardGibbsenergyofformation 9 2Severalrelations 1 relationofreactionGibbsenergy rGm tothechemicalpotentialsofthespecies rGm products reactants 2 Thestandardequilibriumconstant K andthestandardreactionGibbsenergy RTInKo 3 generalexpressionfor rGmatanarbitrarystageofthereaction rGm RTInQ 10 Review 5 thermodynamicequilibriumconstant 热力学平衡常数 canexpressedintermsofactivities orfugacities KforPerfectgasreaction solutionreactionandheterogeneousreactionhasdifferentform 6 intermsofstandardGibbsenergiesofformation 11 Thecontentforthisclass 1ThestandardGibbsenergyofreactioninsolution2Theresponseofequilibriatotheconditions 1 Howequilibriarespondtopressure 2 Theeffectofinertgasonequilibria 3 LeChatelier sprinciple 4 Theresponseofequilibriatotemperature van tHoffequation 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 3andthesolutionsubmitHenry slawhypothetical 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 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 16 LeChatelier sprinciple Asystematequilibrium whensubjectedtoadisturbance respondsinawaythattendstominimizetheeffectofthedisturbance Theprincipleimpliesthatifasystematequilibriumiscompressed thenthereactionwilladjustsoastominimizetheincreaseinpressure 17 2 effectofinertgas 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 4 Theresponseofequilibriatotemperature AccordingtoLeChatelier sprinciple asystematequilibriumwilltendtoshiftintheendothermicdirectionifthetemperatureisraised whiletheequilibriumtendtoshiftintheexothermicdirectionifthetemperatureislowered 21 Thevan tHoffequation Thevan tHoffequationisanexpressionfortheeffectoftemperatureonthestandardequilibriumconstantKo HereisthestandardreactionenthapyatthetemperatureT 22 thevalueofKatdifferenttemperature General theintegral 积分 ofVan tHoffEquationisusedforgasreactionwhichthepressureislow 1 Ifvariesonlyslightlywithtemperatureoverthetemperaturerangeofinterest theintegralofequationfromT1toT2yiels 23 2 Ifdependsontemperature Specially whentheheatcapacities 热容 ofreactantsandproductsisthemeanvalue thevalueofisconstant then 24 3 Theeffectofinitialcompositiononequilibrium Forexample considertheequil