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ElectrochemistryChapter20opyright2019,PRENTICEHALLElectrochemistry1Oxidation-ReductionReactions·Znaddedtohciyields产量thespontaneous自发的reactionZn(s)+2H*(ag)->Zn(aq)+H2(g).Theoxidationinumberofznhasincreasedfrom0to2+Theoxidationnumberofhhasreducedfrom1+to0ThereforeZnisoxidizedtozn2+whileh+isreducedtohH+causesZntobeoxidizedandistheoxidizingagent.ZncausesH+tobereducedandisthereducingagentNotethatthereducingagentisoxidizedandtheoxidizingagentisreduced.opyright2019,PRENTICEHALLOxidation-ReductionReactions2BalancingOxidation-ReductionEquationsLawofconservationofmass:theamountofeachelementpresentatthebeginningofthereactionmustvbepresentattheendConservationofcharge:electronsarenotlostinachemicalreactionIncomplicatedredox氧化还原作用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无机化学英文版课件11无机化学英文版课件12无机化学英文版课件13无机化学英文版课件14无机化学英文版课件15无机化学英文版课件16无机化学英文版课件17无机化学英文版课件18无机化学英文版课件19无机化学英文版课件20无机化学英文版课件21无机化学英文版课件22无机化学英文版课件23无机化学英文版课件24无机化学英文版课件25无机化学英文版课件26无机化学英文版课件27无机化学英文版课件28无机化学英文版课件29无机化学英文版课件30无机化学英文版课件31无机化学英文版课件32无机化学英文版课件33无机化学英文版课件34无机化学英文版课件35无机化学英文版课件36无机化学英文版课件37无机化学英文版课件38无机化学英文版课件39无机化学英文版课件40无机化学英文版课件41无机化学英文版课件42无机化学英文版课件43