Q. Standard entropies of X₂, Y₂ and XY₃ are 60, 40 and 50 J K⁻¹ mol⁻¹ respectively. For the reaction (1/2)X₂ + (3/2)Y₂ ⇌ XY₃, ΔH = −30 kJ to be at equilibrium, the temperature should be

A) 500 K
B) 750 K
C) 1000 K
D) 1250 K
Explanation

[Solution from source] ΔS° = 50 − (½ × 60 + 3/2 × 40) = 50 − 90 = −40 J K⁻¹ mol⁻¹. At equilibrium ΔG = 0, so T = ΔH/ΔS = (−30000)/(−40) = 750 K. Forgetting the stoichiometric halves gives a different ΔS and a wrong T. Answer (2).

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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