Question

Under what condition can Al reduce MgO?

(a) Above 1000°C

(b) Below 1000°C

(c) Above 1350°C

(d) Below 1350°C

I got this question during an interview.

The origin of the question is Thermodynamic Principles of Metallurgy in chapter General Principles and Processes of Isolation of Elements of Chemistry – Class 12

Answer 1

Correct answer is (c) Above 1350°C

Easiest explanation: For a reaction to be feasible, the change in the Gibbs free energy of the reaction (Δ G) must be negative. Lesser the ΔG, greater is the feasibility of the reaction. Above 1350°C, the standard Gibbs free energy of formation of Al2O3 from Al is less than that of MgO from Mg. Therefore, Al can reduce MgO above 1350°C.