Gases can be converted to liquids by compressing the gas at a suitable temperature.
Gases become more difficult to liquefy as the temperature increases because the kinetic energies of the particles that make up the gas also increase.
The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.
Every substance has a critical temperature. Some examples are shown below.
The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature. Some examples are shown below.
Importance of critical temperatureCritical temperature of gas provides insight into strength of intermolecular attraction forces that its particles are subject.
A gaseous substance with relatively weak intermolecular forces will be more difficult to liquefy than a gaseous substance with a stronger intermolecular attraction. Therefore, the weaker the intermolecular force, the lower the critical temperature.
Difference between Triple Point and Critical Point
The critical point between the liquid phase and the vapour phase defines the conditions under which a liquid substance can coexist with its vapour
Triple point of a substance is the temperature and pressure at which it can exist in three states. A substance is said to be at its critical point when the absolute temperature associated with it is equal to its critical temperature and pressure applied to it is equal to its critical pressure.