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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

Q2. Critical constants of a van der Waals gas and Zc

Question

Write the equation that relates van der Waals constants a and b to critical temperature and critical pressure. Using the values of Tc, Pc and Vc thus obtained in terms of a and b, find the value of critical compressibility factor (Zc).

Answer in brief

Vc = 3b, Tc = 8a/27Rb, Pc = a/27b²; a = 27R²Tc²/64Pc, b = RTc/8Pc. Zc = 3/8 = 0.375.

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Topic notes: real gases, the van der Waals equation, critical constants and Boyle temperature, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverscritical constantsvan der Waals gascritical compressibility factorpoint of inflexionZc = 3/8