NCERT Class XI Chemistry Thermodynamics Solutions

Question : 19

Total: 22

For the reaction, 2A(g)+B(g) → 2D(g), ΔU° = –10.5 kJ and ΔS° = – 44.1 JK–1. Calculate ΔG° for the reaction, and predict whether the reaction may occur spontaneously.

Solution:

ΔH° = ΔU° + ΔngRT, ΔU° = –10.5 kJmol–1, R = 8.314 JK–1mol–1, T = 298 K Δng = 2 – (2 + 1) = –1
∴ ΔH° = –10.5 – (1) × 8.314 × 10–3 × 298 = –10.5 – 2.48 = –12.98 kJmol–1
Now ΔG° = ΔH° – TΔS° = –12.98 – 298 × (–44.1 × 10–3)
= –12.98 +13.14 = 0.16 kJmol–1
Since DG° is positive, the reaction is not spontaneous.

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