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Question
Answer the following questions based on the P–T phase diagram of CO2:
CO2 at 1 atm pressure and temperature – 60 °C is compressed isothermally. Does it go through a liquid phase?
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Solution 1
No
The P-T phase diagram for CO2 is shown in the following figure.
At 1 atm pressure and at –60°C, CO2 lies to the left of –56.6°C (triple point C). Hence, it lies in the region of vaporous and solid phases.
Thus, CO2 condenses into the solid state directly, without going through the liquid state
Solution 2
No, the CO2 does not go through the liquid phase. The point (1.00 atm, – 60°C) is to the lift of the triple-point O and below the sublimation curve OA. Therefore, when CO2 is compressed at this point at constant temperature, the point moves perpendicular to the temperature-axis and enters the solid phase region. Hence, the CO2 vapour condenses to solid directly without going through the liquid phase.
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