Low temperature and high pressure are the two main condition for the liquefaction of gases. The pressure and temperature which are applying will depend on the molecular force of the gas molecules. There is a limit to the temperature where the pressure is to be applied for the liquefication of the gas which is called critical temperature. There are three methods apart from this.
- Compressing the gas at temperature less than its critical temperature
- Application of an external force
- Making the gas to do work against its own internal forces so that it loses energy and liquifies.