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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper I

Q3(d). Phase diagram of water; critical point and triple point

Question

Construct a phase-diagram for a one component system (water) and explain all the three curves. Also describe the significance of critical pressure, critical temperature and triple point.

Answer in brief

The vaporisation curve OA, the sublimation curve OB and the fusion curve OC meet at the triple point O (273.16 K, 4.58 torr); OA ends at the critical point A (647 K, 218 atm).

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Topic notes: the phase rule, phase diagrams, the Clausius–Clapeyron equation, eutectics and partially miscible liquids, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversphase diagram of waterphase ruletriple pointcritical pointClapeyron equationsublimation curve

All parts of Question 3