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GATE 2022 CY – Question 31

Physical Chemistry · Phase Equilibria: Phase rule. Clausius- Clapeyron equation. Phase diagram of one component system: CO2, H2O, S; two component systems: liquid-vapor, liquid-liquid and solid-liquid systems. Fractional distillation. Azeotropes and Eutectics. · 1 mark · Multiple select

The CORRECT statement(s) about the following phase diagram for a hypothetical pure substance X is(are)

Diagram for GATE 2022 CY question 31
  1. The molar volume of solid X is less than the molar volume of liquid X
  2. X does not have a normal boiling point
  3. The melting point of X decreases with increase in pressure
  4. On increasing the pressure of the gas isothermally, it is impossible to reach solid phase before reaching liquid phase

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Correct answer: (B) X does not have a normal boiling point; (C) The melting point of X decreases with increase in pressure

Explanation

The triple-point pressure is above 1 atm, so the 1-atm line never reaches liquid–vapour equilibrium: there is no normal boiling point, B. The negative melting-line slope means melting temperature decreases as pressure increases, C. Clapeyron then implies liquid volume is smaller than solid volume, contradicting A. Below the triple-point temperature, compression can reach solid directly, so D is false. **B, C**.