Question

 Following reactions occur at cathode during the electrolysis of aqueous copper(II) chloride solution :

On the basis of their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why ?

Answer 1

\[{Cu}^{2 +} \left( aq \right) + 2 e^- \to Cu\left( s \right) E^{\circ} = + 0 . 34 V\]
\[ H^+ \left( aq \right) + e^- \to \frac{1}{2} H_2 \left( g \right) E^{\circ} = 0 . 00 V\]

The relationship between the standard free energy change and the standard emf of a cell reaction is given by 

ΔG°=−nFE

Thus, the more positive the standard reduction potential of a reaction, the more negative is the standard free energy change associated with the process and, consequently, the higher is the feasibility of the reaction.

Since E∘Cu2+/CuECu2+/Cu° has a greater positive value than E∘H+/HEH+/H°, the reaction that is feasible at the cathode is

Cu2+(aq) + 2e− → Cu(s)