Question
Derive the relationship between standard cell potential and equilibrium constant of cell reaction.

Answer

The relation between standard Gibbs energy change of cell reaction and standard cell potential is given by
$
-\Delta G ^{\circ}=- nF E _{\text {cell }}^{\circ} \cdots(1)
$

The relation between standard Gibbs energy change of a chemical reaction and its equilibrium constant as given in thermodynamics is:
$
\Delta G^{\circ}=-R T \ln K \cdots(2)
$

Combining equations (1) and (2), we have
$
-n F E_{\text {cell }}^{\circ}=- RT \ln K
$
$
\therefore E _{\text {cell }}^{\circ}=\frac{ RT }{ nF } \ln K
$
$
=\frac{2.303 RT }{ nF } \log _{10} K
$
$
=\frac{0.0592}{ n } \log _{10} K \text { at } 25^{\circ} C
$

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