Question

Answer the following questions based on the P-T phase diagram of CO₂: 

1. CO₂ at 1 atm pressure and temperature – 60°C is compressed isothermally. Does it go through a liquid phase? 

2. What happens when CO₂ at 4 atm pressure is cooled from room temperature at constant pressure? 

3. Describe qualitatively the changes In a given mass of solid CO₂ at 10 atm pressure and temperature -65°C as it is heated up to room temperature at constant pressure. 

4. CO₂ is heated to a temperature 700C and compressed isothermally. What changes in its properties do you expect to observe?

Answer 1

1. When subjected to isothermal compression, CO₂ will condense to solid directly without passing through the liquid phase. 

2. When cooled at constant pressure, CO₂ will condense directly to solid phase without passing through the liquid phase, 

3. As the solid CO₂ is heated up, it first turns to liquid phase and then solid phase. The fusion and boiling points can be obtained from finding out the points of intersection between the horizontal 10 atm line on the P-T diagram with the fusion and vaporisation curves. 

4. CO₂ will not exhibit any clear transition to the liquid phase but will deviate more and more from ideal behaviour ps the pressure increases.