Question

The Gibbs energy for the decomposition of $A{l}_2{O}_3$ at ${500}^{\circ }C$ is as follows:
$\frac{2}{3}A{l}_2{O}_3\to \frac{4}{3}Al+O_2;{△}_{r}G=+966kJmo{l}^{-1}$
The potential difference needed for the electrolytic reduction of $A{l}_2{O}_3$ at ${500}^{\circ }$ is at least.

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

Answer 1

The correct option is A $2.5V$

In the given reaction,
$\frac{2}{3}\left[2A{l}^{3+}\right]+4e\to \frac{4}{3}Al(n=4)$
$\therefore △G=-nFE$
$E=\frac{△G}{nF}=-\frac{966\times 1000}{4\times 96500}$
$=-2.5V$.