For the reaction $2{\text{Fe}}^{3+}+2{\text{I}}^{-}\to 2{\text{Fe}}^{2+}+{\text{I}}_2$, the standard EMF is $0.236\text{ V}$ at $298\text{ K}$. Calculate the equilibrium constant $K_c$.

Solution

1. The number of electrons transferred $n=2$.
2. The relation is $\log K_c=n{E}^{\circ }/0.0591$.
3. $$\begin{array}{rl}\log K_c& =(2\times 0.236)/0.0591\\ & =0.472/0.0591\approx 7.986\end{array}$$.
4. $K_c=10^{7.986}\approx 9.68\times 10^7\approx 1.2\times 10^8$.
5. Hence the answer is (A).