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Question:

The plot shows the variation of −lnKp versus temperature for the two reactions: M(s) + 1/2O2(g) → MO(s) and C(s) + 1/2O2(g) → CO(s). Identify the correct statement.

At T < 1200K, the reaction MO(s) + C(s) → M(s) + CO(g) is spontaneous.

Oxidation of carbon is favourable at all temperatures.

At T > 1200K, carbon will reduce MO(s) to M(s).

At T < 1200K, oxidation of carbon is unfavourable.

Solution:

At T > 1200K, carbon will reduce MO(s) to M(s).
ΔG° = −RTlnKp
lnKp = ΔG°/RT
ΔG° ∝ Temperature
At high temperature ΔG° value is very high so a non-feasible or non-spontaneous process takes place and carbon will reduce MO(s) to M(s). Hence, option C is correct.