Question

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

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

Answer 1

Answer: (C)

$2.5V$

$\Delta G=-nFE$ $=E=\frac{-\Delta G}{nF}$
$E=-\frac{966\times {10}^3}{4\times 96500}$$=-2.5V$
The potential difference needed for the reduction$=2.5V$.