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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 · 2016 · Mains Paper II

Q10(b). Reversible expansion of a real gas

Question

Deduce expressions for work W, internal-energy change ΔU and enthalpy change ΔH for reversible expansion of a van der Waals gas from V₁ to V₂.

Answer in brief

For one mole undergoing isothermal reversible expansion, use p=RT/(V-b)-a/V². With work on the gas positive, w=-RTln [(V₂-b)/(V₁-b)]+a(1/V₁-1/V₂).

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CoversReversible expansion of a real gasThermodynamics

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