electrode-potential-and-cells电极电位和细胞

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1、ELECTRODEPOTENTIALANDCELLS:INTRODUCTION:Importantclassofchemicalreactionsisoxidation-reductionreactions.Inoxidation:aspecieslosesoneormoreelectronsresultinginanincreaseinitsoxidationnumber.MMn++ne-Inreduction:thespeciesgainsoneormoreelectrons,thereisadecreasei

2、noxidationnumber.Mn++ne-MAreductionprocessnecessarilyaccompaniesanoxidationprocesssinceelectronscanbelostbyaspeciesonlywhenthereisacounterparttoreceivethem.Redoxreactionformsthebasisofelectrochemicalcells.Anelectrochemicalcellconsistsoftwoelectrodeswhichwhenco

3、nnectedbyametallicwire:anelectriccurrentflowsasaresultofaspontaneousredoxreaction.Eachelectrodeusuallyconsistsofametalincontactwithasolutionofitsownion.Sinceacellisacombinationoftwoelectrodes,eachelectrodeisreferredtoasasingleelectrodeorhalf-cell.Apotentialcal

4、ledtheelectrodepotentialarisesattheelectrodeincontactwithitsionicsolution.Thedifferencebetweenthepotentialsofthetwohalf-cellsconstitutestheelectromotiveforce(emf)ofthecell.Emf:“Thevoltageundertheinfluenceofwhichtheelectriccurrentflowsinthecelliscalledtheelectr

5、omotiveforceofthecellortheemfofthecell”ELECTROCHEMICALCELLS:Definition:Electrochemicalcellisadeviceinwhichchemicalenergyisconvertedintoelectricalenergyorelectricalenergyintochemicalenergybyoxidation-reductionreaction.Thus,therecanbetwotypesofElectrochemicalcel

6、ls.1.Galvaniccellorvoltaiccell:theone,whichconvertschemicalenergyintoelectricalenergy.2.Electrolyticcell:theone,whichconvertselectricalenergyintochemicalenergy.GALVANICCELL:AtypicalegsofgalvaniccellisDanielcell,whichisillustratedinthefig.CONSTRUCTIONANDWORKING

7、:Itconsistsoftwobeakersoneofwhichcontainszincrodimmersedinzincsulphatesolutionandtheotheronecontainscopperrodincoppersulphatesolution.Asaltbridgeconnectsthesolutionsoftwobeakers.Thezincandcopperrodsareconnectedexternallythroughvoltmeterbyusingawire.Oncompletin

8、gthecircuitthefollowingchangesareobserved1.zincrodstartsdissolve2.coppergetsdepositedoncopperrod3.zincsulphatesolutionbecomesmoreconcentratedwithrespecttoZn2+ions4.coppersulphateso