Answer the following questions based on the P-T phase diagram of carbon dioxide:
(a) At what temperature and pressure can the solid, liquid and vapour phases of CO2 co-exist in equilibrium?
(b) What is the effect of decrease of pressure on the fusion and boiling point of
CO2?
(c) What are the critical temperature and pressure for CO2? What is their significance?
(d) Is CO2 solid, liquid or gas at (a) –70 °C under 1 atm, (b) –60 °C under 10 atm, (c) 15 °C under 56 atm?
The P-T phase diagram of CO2 is as follows:
(a) The solid, liquid and vapour phase of carbon dioxide exist in equilibrium at the triple point, i.e., the point corresponding to the temperature value of - 56.7° C and pressure value of 5.1 atm.
(b) With the decrease in pressure, both the fusion and boiling point of carbon dioxide will decrease.
(c) For carbon dioxide, the critical temperature is 31°C and critical pressure is 72.9 atm. If the temperature of carbon dioxide is more than 31° C, it cannot be liquified irrespective of the applied pressure.
(d) Carbon dioxide will be a vapour at 70°C under 1 atm, a solid at -6°C under 10 atm and a liquid at 15°C under 56 atm.