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?
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
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.