Q. The Gibbs energy for the decomposition of Al₂O₃ at 500°C is as follows: (2/3)Al₂O₃ → (4/3)Al + O₂; ΔrG = +960 kJ mol⁻¹ The potential difference needed for the electrolytic reduction of aluminium oxide (Al₂O₃) at 500°C is at least
A) 4.5 V
B) 3.0 V
C) 2.5 V
D) 5.0 V
Explanation
[Solution from source] Making 4/3 mol Al from Al³⁺ needs (4/3) × 3 = 4 mol electrons per mol O₂. E = ΔG/(nF) = 960000/(4 × 96500) ≈ 2.5 V. Taking n = 3 instead would give about 3.3 V. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.