Question

The Gibbs energy for the decomposition of Al2O3 at 500ŗC is as follows :

$\frac{2}{3}Al_{2}O_{3} \rightarrow \frac{4}{3}Al + O_{2};\Delta_{r}G = + 966kJmol^{- 1}.$ The potential difference needed for electrolytic reduction of Al2O3 at 500⁰C is at least :

• A. 4.5 V
• B. 3.0 V
• C. 2.5 V
• D. 5.0 V

Answer 1

Answer: (C)

2.5 V

Answer 2

$\frac{2}{3}Al_{2}O_{3}\overset{\quad\quad}{\rightarrow}\frac{4}{3}Al + O_{2}$

$\Delta\text{G = +966 kJ mo}\text{l}^{\text{-1}}\text{ = 966 }\text{×}\text{ 103 J mo}\text{l}^{\text{-1}}\$

$\Delta\text{G = - nF}\text{E}_{\text{cell}}\$ $966 \times 10 ^ { 3 } = - 4 \times 96500 \times \mathrm { E } _ { \text {cell } }$ $E_{\text{cell}}\text{ = 2.5 V}$