电化学热力学7-7

§7-7电极电势和电池电动势一、标准氢电极和标准电极电势1、标准氢电极Pt),,(p.gH|)1(H2Hpa)(H21e)1(H2Hpa任何温度下标准氢电极的电极电势均为零0Pt,/HH2E规定：即2、标准电极电势给定电极||)1(H|),(p.gH|PtH2ap液接电势已消除，则EEEE若给定电极处于其标准态下，则EEEEAg(s)|)1(Ag||)1(H|),(p.gH|PtAgH2aap例如原电池AgAgEEE则说明1、课本表中给出的数据都是还原电极电势Ag,AgE注意写法,AgAgE2、氢电极以上各电极电势为负值，表明它们与标准氢电极组成电池后，氢电极所发生的反应为还原反应；氢电极以下各电极电势为正值，表明它们与标准氢电极组成电池后，氢电极所发生的反应为氧化反应。3、对于给定的电极，标准态选定后，二、电极电势与浓度的关系)Ag(s|)(Ag||)00.1(H|)(H|PtAgH2aap例如原电池)(TfE2Ag(s)2e)(2AgAga)Ag(s2)00.1(2H)(2Ag)(HHAg2aap负极反应2e)00.1(2H)(HH2ap正极反应电池反应Nernst方程：aQzFRTEEln2Ag2H2Ag..ln22HaaaFRTEppAgAglnaaFRTEAgAg2HHAgAgEEEE而AgAg2HHAgAgEEEE则AgAglnAgAgAgAgaaFRTEE氧还aaFRTElnAgAg∴电极电势的Nernst方程lnlnxyaaRTRTEEEzFazFa氧还电极电极还氧例如Cu(s))(Cu2Cu2a222CuCuCu,CuCu,Culn2aaFRTEEAg(s)AgCl(s)|)(ClCla)(ClAg(s)eAgCl(s)ClaClAgAgCl.lnAgAgClClAgAgClClaaaFRTEE又如Pt),(O|OH2O2p2OHO2H2e)(O212O22p再如电极反应电极反应2OH2/1O)/(ln22Pt,2OOHPt,2OOHppFRTEE三、电极电势与电池电动势的计算小结电极电势电池电动势zFEGmrzEFGmrzFEGmrzFEGmr氧还aazFRTEElnEEQzFRTEEaln298.15KCu|)047.0,kgmol0.1(CuSO||)734.0,kgmol001.0(ZnSO|Zn124114γbγb3402.0,7628.0Cu2CuZn2ZnEE求该电池电动势E。例1Cu2eCu2解Ⅰ2eZnZn2负极反应正极反应电池反应22ZnCuCuZn∴22CuZnln2aaFRTEECuSO4溶液047.0,kgmol0.111γbγγγ设047.00.1047.02Cubbγa则同理3Zn10734.02aV156.122Zn2ZnCu2CuCuZnln2aaFRTEEEV047.010734.0ln96500215.298314.8)7628.0(3402.03解Ⅱ2Cu2CuCu2CuCuln2aFRTEEV3009.0V047.0ln96500215.298314.83402.02Zn2ZnZn2ZnZnln2aFRTEEV10734.0ln96500215.298314.87628.03V8554.0VEEEZnZnCuCu156.122V065.1,V7994.0Pt,2BrBrAgAgEE?)(AgBr?;mfAgAgBrBrGE?AgAgBrBrE例2已知25ºC时AgBr在纯水中的溶度积,1086.413spK并已知试求解：①求BrAg(s)eAgBr(s)AgAgBrBrm,1rFEG⑵⑴Ag(s)eAg⑶AgAgm,2rFEGBrAgAgBr(s)spKRTGlnm,3r⑴–⑵=⑶,则m,3rm,2rm,1rGGGsplnAgAgAgAgBrBrKRTFEFEV7994.0965001086.4ln15.298314.813∴AgAgAgAgBrBrlnEFKRTEspV0711.0②)AgBr(s(l)Br21Ag(s)2设计成原电池)Pt(s(l),Br|)(Br|AgBr(s)Ag(s)2Bra212BrAgAgBrlnaaaFRTEEEAgAgBrBrPt,2BrBrEEV9939.0V)0711.0065.1(1molkJ91.95Pt),1(OS),(SO||)(SO|(s)PbSOPb(s)22821241244aaa)B(mfBmrGvG)(AgBrmfGFzE13mfmolJ)10965009939.01()(AgBrG例3已知下述电池V126.0,1067.1Pb2Pb8spEK电动势的温度系数14KV109.4)TEp（且知该电池在25ºC时以1V工作电压不可逆放电（放电量为1F）放热151.6kJ。已知25ºC时PbSO4的活度积（1）写出电池反应；（2）求算?Pb4PbSO24SOE（3）求该可逆电池的电动势；（4）计算活度a1(SO42-)。V01.2Pt24SO,28O2SE)(SO(s)PbSO)1(OSPb(s)12442282aa解：⑴2e(s)PbSO)(SOPb(s)4124a负极反应正极反应)(2SO2e)1(OS1242282aa电池反应⑵sp2424)1SOPb(s)PbSOKPbPbE2)2Pb(s)2ePb2EPb,PbSOSO244424)3SOPb(s)2e(s)PbSOm3rm2rm1r)3)2)1GGGEEzFzFKRTPb,PbSOSOPbPbsp4242lnV3559.0EEKzFRTPbPbspPbPbSOSO2424lnV126.09650021067.1ln15.298314.88⑶13molJ)101965006.151(fmrWQU1molkJ1.248RTvHUBmrmr1mrmolkJ1.248HpTEzFTzEFHmr而V)109.4(298965001)101.248(43zFTEzFTHEp)(mr∴V425.2⑷由Nernst方程28224OSSOlnaazFRTEE28224Pb4PbSO24SO24282OSSO/PtSO,OSlnaazFRTEE01.024SOa1ln965002298314.8)3559.0(01.2425.224SOa解之