ElectrochemistryChapter20opyright2019,PRENTICEHALLElectrochemistry1Oxidation-ReductionReactions·Znaddedtohciyields產(chǎn)量thespontaneous自發(fā)的reactionZn(s)+2H*(ag)->Zn(aq)+H2(g).Theoxidationinumberofznhasincreasedfrom0to2+Theoxidationnumberofhhasreducedfrom1+to0ThereforeZnisoxidizedtozn2+whileh+isreducedtohH+causesZntobeoxidizedandistheoxidizingagent.ZncausesH+tobereducedandisthereducingagentNotethatthereducingagentisoxidizedandtheoxidizingagentisreduced.opyright2019,PRENTICEHALLOxidation-ReductionReactions2BalancingOxidation-ReductionEquationsLawofconservationofmass:theamountofeachelementpresentatthebeginningofthereactionmustvbepresentattheendConservationofcharge:electronsarenotlostinachemicalreactionIncomplicatedredox氧化還原作用reactions,weneedtolookatthetransferofelectronscarefullyHalf-ReactionsHalf-reactionsareaconvenientwayofseparatingoxidationandreductionreactionsopyright2019,PRENTICEHALLBalancingOxidation-Reduction3BalancingOxidation-ReductionEquationsHalf-ReactionsThehalf-reactionsforSn*(aq)+2Fe(ag)->Sn*(ag)+2Fest(aq)areSn2aq)→Sn4(aq)+2e2Fe3+(ag)+2e-+2Fe+(ag)Oxidation:electronsareproductsReduction:electronsarereagentsopyright2019,PRENTICEHALLBalancingOxidation-Reduction4BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsConsiderthetitrationofanacidicsolutionofNa2C2O4sodiumoxalate,colorless)withKMnO4(deeppurple).MnOaisreducedtoMn+(palepink)whiletheC2O42isoxidizedtocoTheequivalencepointisgivenbythepresenceofapalepinkcolor.IfmoreKMnO4isadded,thesolutionturnspurpleduetotheexcessKMnO4Copyright2019,PRENTICEHALLBalancingOxidation-Reduction5BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsCopyright2019,PRENTICEHALLBalancingOxidation-Reduction6BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsWhatisthebalancedchemicalequation?1.Writedownthetwohalfreactions2.BalanceeachhalfreactionaFirstwithelementsotherthanhandob.ThenbalanceobyaddingwaterCThenbalanceHbyaddinghd.Finishbybalancingchargebyaddingelectrons.Copyright2019,PRENTICEHALLBalancingOxidation-Reduction7BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-Reactions3.Multiplyeachhalfreactiontomakethenumberofelectronsequal4.Addthereactionsandsimplify5.Check!ForKMno+nac,oCopyright2019,PRENTICEHALLBalancingOxidation-Reduction8BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-Reactions1.ThetwoincompletehalfreactionsareMnO4(ag)->Mn+(aq)C2O42(aq)→2CO2(g)2.Addingwaterandh+yields8H*++MnO4(ag)>Mn(aq)+4H,OThereisachargeof7+ontheleftand2+ontheright.Therefore.5electronsneedtobeaddedtotheleftSe+8H++MnO4(ag)->Mn+(aq)+4H,OCopyright2019,PRENTICEHALLBalancingOxidation-Reduction9BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsIntheoxalatereaction,thereisa2-chargeontheleftandaochargeontheright,soweneedtoaddtwoelectronsC204(aq)>2CO2(g)+2e3.Tobalancethe5electronsforpermanganateand2electronsforoxalate.weneed10electronsforbothMultiplyinggivesCopyright2019,PRENTICEHALLBalancingOxidation-Reduction10無機化學(xué)英文版課件11無機化學(xué)英文版課件12無機化學(xué)英文版課件13無機化學(xué)英文版課件14無機化學(xué)英文版課件15無機化學(xué)英文版課件16無機化學(xué)英文版課件17無機化學(xué)英文版課件18無機化學(xué)英文版課件19無機化學(xué)英文版課件20無機化學(xué)英文版課件21無機化學(xué)英文版課件22無機化學(xué)英文版課件23無機化學(xué)英文版課件24無機化學(xué)英文版課件25無機化學(xué)英文版課件26無機化學(xué)英文版課件27無機化學(xué)英文版課件28無機化學(xué)英文版課件29無機化學(xué)英文版課件30無機化學(xué)英文版課件31無機化學(xué)英文版課件32無機化學(xué)英文版課件33無機化學(xué)英文版課件34無機化學(xué)英文版課件35無機化學(xué)英文版課件36無機化學(xué)英文版課件37無機化學(xué)英文版課件38無機化學(xué)英文版課件39無機化學(xué)英文版課件40無機化學(xué)英文版課件41無機化學(xué)英文版課件42無機化學(xué)英文版課件43無機化學(xué)英文版課件44無機化學(xué)英文版課件45無機化學(xué)英文版課件46無機化學(xué)英文版課件47無機化學(xué)英文版課件48無機化學(xué)英文版課件49無機化學(xué)英文版課件50無機化學(xué)英文版課件51無機化學(xué)英文版課件52無機化學(xué)英文版課件53無機化學(xué)英文版課件54無機化學(xué)英文版課件55無機化學(xué)英文版課件56無機化學(xué)英文版課件57無機化學(xué)英文版課件58無機化學(xué)英文版課件59ElectrochemistryChapter20opyright2019,PRENTICEHALLElectrochemistry60Oxidation-ReductionReactions·Znaddedtohciyields產(chǎn)量thespontaneous自發(fā)的reactionZn(s)+2H*(ag)->Zn(aq)+H2(g).Theoxidationinumberofznhasincreasedfrom0to2+Theoxidationnumberofhhasreducedfrom1+to0ThereforeZnisoxidizedtozn2+whileh+isreducedtohH+causesZntobeoxidizedandistheoxidizingagent.ZncausesH+tobereducedandisthereducingagentNotethatthereducingagentisoxidizedandtheoxidizingagentisreduced.opyright2019,PRENTICEHALLOxidation-ReductionReactions61BalancingOxidation-ReductionEquationsLawofconservationofmass:theamountofeachelementpresentatthebeginningofthereactionmustvbepresentattheendConservationofcharge:electronsarenotlostinachemicalreactionIncomplicatedredox氧化還原作用reactions,weneedtolookatthetransferofelectronscarefullyHalf-ReactionsHalf-reactionsareaconvenientwayofseparatingoxidationandreductionreactionsopyright2019,PRENTICEHALLBalancingOxidation-Reduction62BalancingOxidation-ReductionEquationsHalf-ReactionsThehalf-reactionsforSn*(aq)+2Fe(ag)->Sn*(ag)+2Fest(aq)areSn2aq)→Sn4(aq)+2e2Fe3+(ag)+2e-+2Fe+(ag)Oxidation:electronsareproductsReduction:electronsarereagentsopyright2019,PRENTICEHALLBalancingOxidation-Reduction63BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsConsiderthetitrationofanacidicsolutionofNa2C2O4sodiumoxalate,colorless)withKMnO4(deeppurple).MnOaisreducedtoMn+(palepink)whiletheC2O42isoxidizedtocoTheequivalencepointisgivenbythepresenceofapalepinkcolor.IfmoreKMnO4isadded,thesolutionturnspurpleduetotheexcessKMnO4Copyright2019,PRENTICEHALLBalancingOxidation-Reduction64BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsCopyright2019,PRENTICEHALLBalancingOxidation-Reduction65BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsWhatisthebalancedchemicalequation?1.Writedownthetwohalfreactions2.BalanceeachhalfreactionaFirstwithelementsotherthanhandob.ThenbalanceobyaddingwaterCThenbalanceHbyaddinghd.Finishbybalancingchargebyaddingelectrons.Copyright2019,PRENTICEHALLBalancingOxidation-Reduction66BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-Reactions3.Multiplyeachhalfreactiontomakethenumberofelectronsequal4.Addthereactionsandsimplify5.Check!ForKMno+nac,oCopyright2019,PRENTICEHALLBalancingOxidation-Reduction67BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-Reactions1.ThetwoincompletehalfreactionsareMnO4(ag)->Mn+(aq)C2O42(aq)→2CO2(g)2.Addingwaterandh+yields8H*++MnO4(ag)>Mn(aq)+4H,OThereisachargeof7+ontheleftand2+ontheright.Therefore.5electronsneedtobeaddedtotheleftSe+8H++MnO4(ag)->Mn+(aq)+4H,OCopyright2019,PRENTICEHALLBalancingOxidation-Reduction68BalancingOxidation-ReductionEquationsBalancingEquationsbytheMethodofHalf-ReactionsIntheoxalatereaction,thereisa2-chargeontheleftandaochargeontheright,soweneedtoaddtwoelectronsC204(aq)>2CO2(g)+2e3