Explain the liquefication of gases.

Explanation

Liquification of gases can be done by decreasing the temperature and increasing the pressure.
Liquefaction of gases: Any gas, if it to be liquefied, it must be cooled below its critical temperature. A gas liquefies if it is cooled below its boiling point at given pressure. For example, chlorine at room pressure say 1 atmosphere can be liquefied by cooling it to `- 34.0^@ C` in a dry ice bath. For `N_2` and `O_2` that have very low boiling points -` 196^@ C and -183^@ C` Such simple technique is not possible. Then, to liquify such type of gases the technique based on intermolecular forces is used. It is as • follows. If the velocities of molecules are reduced to such lower values that neighbours can attract each other by their interaction or intermolecular attractions, then the cooled gas will condense to a liquid. For this, the molecules are allowed to expand into available volume without supplying any heat from outside. In this, the molecules have to overcome the attractions of their neighbours and in doing so, the molecules convert some of their kinetic energy into potential energy and (now travel slowly. The average velocity decreases and therefore the temperature of the gas decreases and the gas cools down compared to its temperature before its expansion. For this the gas is allowed to expand through a narrow opening called throttle. This way of cooling of gas by expansion from high pressure side to low pressure is called Joule - Thomson effect.