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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper II covers physical chemistry.

UPSC Combined Geo-Scientist, Mains · 2023 · Mains Paper II

Q4. ΔG° and ΔS° from an equilibrium constant

Question

At 1200 K, the equilibrium constant for the reaction A₂ → 2A is found to be 3.3 × 10⁻³. Calculate ΔG° and ΔS° for this reaction at 1200 K. Given that ΔH° for the reaction is 216.65 kJ mol⁻¹.

Answer in brief

ΔG° = −RT ln K = +57.0 kJ mol⁻¹; ΔS° = (ΔH° − ΔG°)/T = +133.0 J K⁻¹ mol⁻¹.

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Topic notes: chemical equilibrium, ΔG° = −RT ln K, Kp, Kc, Kx and the van ’t Hoff equations, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversstandard Gibbs energyequilibrium constantΔG° = −RT ln Kentropy changevan 't Hoff equation