Question

Following reactions occur at cathode during the electrolysis of aqueous silver chloride solution :

`Ag^+(aq)+e^(-)rarrAg(s)" ""      ""       "E^@=+0.80V`

`H^+(aq)+e^(-)rarr1/2H_2(g)" "" "" " E^@=0.00V`

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

Answer 1

Given :

`Ag^+(aq)+e^(-)rarrAg(s)" ""      ""       "E^@=+0.80V`

`H^+(aq)+e^(-)rarr1/2H_2(g)" "" "" " E^@=0.00V`

The relationship between the standard free energy change and 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∘Ag+/AgE∘Ag+/Ag has a greater positive value than E∘H+/HE∘H+/H, the reaction which is feasible at the cathode is given by 

Ag⁺(aq) + e⁻ → Ag(s)