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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 · 2025 · Mains Paper II

Q11(a). Chemical potential of a real gas relative to an ideal gas

Question

The fugacity coefficient of a certain gas at 200 K and 50 bar is 0.72. Calculate the difference of its chemical potential from that of an ideal gas in the same state.

Answer in brief

μ − μideal = RT ln ϕ = −546 J mol⁻¹ ≈ −0.55 kJ mol⁻¹.

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Topic notes: chemical potential, partial molar quantities, the Gibbs–Duhem equation, fugacity and activity, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversfugacity coefficientchemical potentialreal gasfugacityμ = μ° + RT ln f

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