આપેલ :
$F{e^{2 + }} + 2{e^ - } \to Fe;$ ${E^o}_{F{e^{2 + }}/Fe} = - 0.47\,V$
$F{e^{3 + }} + {e^ - } \to F{e^{2 + }};$ ${E^o}_{F{e^{3 + }}/F{e^{2 + }}} = + 0.77\,V$
$(i)\,F{e^{2 + }}\, + \,2{e^ - }\, \to \,Fe;$ ${E^o}\, = \, - 0.47\,\,V;$
$(ii)\,F{e^{3 + }}\, + \,{e^ - }\, \to \,F{e^{2 + }};$ ${E^o}\, = \, + 0.77\,\,V;$
$(iii)\,F{e^{3 + }}\, + \,3{e^ - }\, \to Fe$
$(i)\,\Delta {G^o}\, = \, - nF{E^o}\, = \, - \,2\,( - 0.47)F\, = \,0.94\,F$
$(ii)\,\Delta {G^o}\, = \, - nF{E^o}\, = \, - \,1\,( + 0.77)F\, = \, - 0.77F$
$(iii)$ on adding $:\,\Delta {G^o}\, = \, + \,0.17\,F$
$\Delta {G^o}\, = \, - nF{E^o}\,{E^o}$ for
$(F{e^{3 + }} \to Fe)\, = \,\frac{{\Delta {G^o}}}{{ - nF}}\,$ $ = \,\frac{{0.17F}}{{ - 3F}}\, = \, - \,0.057\,V$
$Fe_{(aq)}^{3 + } + {e^ - } \to Fe_{(aq)}^{2 + }$ ; ${E^o} = 0.771{\mkern 1mu} \,volts;{\mkern 1mu} $
${\mkern 1mu} {I_{2(g)}} + 2{e^ - } \to 2I_{(aq)}^ - \,;{\mkern 1mu} $ ${E^o} = 0.536{\mkern 1mu} \,volts$
કોષ પક્રિયા $2Fe^{3+}_{(aq)} + 2l^{-}_{(aq)} \rightarrow 2Fe^{2+}_{(aq)} + I_{2(g)}$ માટે $E^o_{cell} = ….$
$Mn^{2+} +2e- \rightarrow Mn;\, E^o = -1.18\,V$
$2(Mn^{3+} +e^- \rightarrow Mn^{2+} )\,;\,E^o=+1.51\,V$
તો $3Mn^{2+} \rightarrow Mn+ 2Mn^{3+}$ માટે $E^o$ કેટલો થશે ?