The GATE Grind

GATE 2021 CY – Question 25

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 phase diagram of CO2 is shown below: The correct statement(s) about CO2 is/are:

Diagram for GATE 2021 CY question 25
  1. Below Tc, it does not exist in liquid state.
  2. Above Tc, it does not exist in liquid state.
  3. At Tc, it can exist in all three phases.
  4. Above T1, it does not exist in solid state.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) Below Tc, it does not exist in liquid state.; (C) At Tc, it can exist in all three phases.

Explanation

Read Tc as the temperature marked at the three-phase junction in this particular figure. Below it, no liquid region exists, so A is true. At the junction, solid, liquid and gas coexist, so C is true. Above it, liquid can exist at suitable pressure, contradicting B; solid can also exist above T1 at sufficiently high pressure, contradicting D. **A,C**.