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Question

1) Answer the following question based on the PT phase diagram of CO2:
A) CO2 at 1atm pressure and temperature 60C is compressed isothermally. Does it go through a liquid phase?

2) Answer the following question based on the PT phase diagram of CO2:
B) What happens when CO2 at 4 atm pressure is cooled from room temperature at constant pressure?

3) Answer the following question based on the PT phase diagram of CO2:
C) Describe qualitatively the changes in a given mass of solid CO2 at 10atm pressure and temperature 65C as it is heated up to room temperature at constant pressure.

4) Answer the following question based on the PT phase diagram of CO2:
D) CO2 is heated to a temperature 70C and compressed isothermally. What changes in its properties do you expect to observe?

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Solution

1) No, it dose not liquefy and condenses to solid directly. At 1 atm pressure and at 60C, CO2 lies ot the left of 56.6C (triple point C). Hence, it lies in the region of vaporous and solid phases. Thus, CO2 condenses into the solid state directly, without going though the liquid state.


2) At 4 atm pressure,CO2 lies below 5.11 atm (triple point C.) Hence, it lies in the region of vaporous and solid phases. Thus , it condenses into the solid state directly , without passing through the liquid state.



3) When the temperature of a mass of solid CO2 (at 10 atm pressure and at 65C) is increased , it changes to the liquid phase and then to the vaporous phase. It forms a line parallel to the temperature axis at 10 atm. The fusion and boiling points are given by the intersection points, where this parallel line cuts the fusion and vaporisation curves.


4) If CO2 is heated to 70C and compressed isothermally, then it will not exhibit any transition to the liquid state. This is because 70C is higher than the critical temperature of CO2. It will remain in the vapour state, but will depart from its ideal behaviour as pressure increases.



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