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The Gibbs energy for the decomposition of Al2O3 at 500°C is as follows: 2/3 Al2O3 → 4/3 Al + O2, ΔG = +966 kJ mol⁻¹ The potential difference needed for electrolytic reduction of Al2O3 at 500°C is at least
- 4.5 V
- 3.0 V
- 2.5 V
- 5.0 V
Correct answer: 2.5 V
Solution
The Gibbs energy change indicates the minimum energy required for the reaction to proceed; the relationship between Gibbs energy and cell potential shows that a positive ΔG corresponds to a negative cell potential. Therefore, to achieve a positive cell potential sufficient for the electrolytic reduction of Al2O3, a minimum potential difference of 2.5 V is necessary to overcome the energy barrier.
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