10. LIQUEFACTION OF GASES

LIQUIFACTION OF GASES

Liquifaction of gases can be achieved either by lowering the temperature or increasing the pressure of the gas simultaneously.
Thomas Andrews plotted isotherms of C0₂ at various temperatures shown in figure.

Critical Temperature (T_c): It is defined as that temperature above which a gas cannot be liquified however high pressure may be applied on the gas.
T_c = 8a/27bR
(Where a and b are van der Waals constants)
Critical Pressure (P_c): It is the pressure required to Liquify the gas at the critical temperature.
Pc = a/27b²
The volume occupied by one mole of the gas at the critical temperature and the critical pressure is called the critical volume (V_c).
For Example. For C0₂ to Liquify.
T_c = 30.98°C
P_c = 73,9 atm.
V_c = 95-6 cm³/mole
All the three are collectively called critical constants.