Consider the systems having liquid-solid interface, (A) copper wire in silver nitrate solution and (B)…
Consider the systems having liquid-solid interface, (A) copper wire in silver nitrate solution and (B)
silver wire in copper sulphate solution.
Predict which interface will show spontaneous reaction, if
$$
E_{\mathrm{Cu}^{2+} / \mathrm{Cu}}^{\circ}=0.34 \mathrm{~V} \text { and } E_{\mathrm{Ag}^{+} / \mathrm{Ag}}^{\circ}=0.80 \mathrm{~V} \text { ? }
$$
Copper-silver nitrate interface
Silver-copper sulphate interface
There will be no spontaneous reaction
Both interfaces will give spontaneous reaction
Solution
Spontaneous reaction can be determined on the basis of Gibbs free energy.
$$
\Delta G^{\circ}=-n F E^{\circ}
$$
$$
\begin{aligned}
& E^{\circ}=E_c^{\circ}-E_A^{\circ} \\
& E_c^{\circ} \text { or } E_{\mathrm{Ag}^{+} / \mathrm{Ag}}^{\circ}=0.80 \mathrm{~V} \\
& E_A^{\circ} \text { or } E_{\mathrm{Cu}^{2+} / \mathrm{Cu}}^{\circ}=0.34 \mathrm{~V} \\
& E^{\circ}=0.80-0.34=0.46 \mathrm{~V} \\
& \Delta G^{\circ}=-n F E^{\circ}=-2 \times 96500 \times 0.46 \mathrm{~V}
\end{aligned}
$$
Hence, $\mathrm{Cu}-\mathrm{Ag}$ nitrate interface show spontaneous reaction due to-ve value of $\Delta G^{\circ}$.
^