Question

The Gibbs energy for the decomposition of Al₂O₃ at 500°C is as follows : $\frac{2}{3} Al_2O_3 \rightarrow \frac{4}{3} Al + O_2$, $\Delta_rG$ = +966kJ mol⁻¹ The potential difference needed for electrolytic reduction of Al₂O₃ at 500°C is at least
(a) 4.5 V
(b) 3.0 V
(c) 2.5 V
(d) 5.0 V

Answer 1

ΔG = - n F Ε°

n = 4 for Aluminum decomposition in to Al and O2. 4 moles of electrons are transferred. F = Faraday = 96500 Coul/mole

E° = - ΔG / n F = - 960 * 1000 /(4 * 96500) = - 2.48 V