What is the principle of liquefaction of gases? Describe any one method used for the liquefaction of gases
Liquefaction of gases is the procedure by which a gas is transformed into a liquid. For example, oxygen usually occurs as a gas. However, by applying enough amounts of pressure and by tumbling the temperature by an adequate amount, oxygen can be changed to a liquid.
In order to liquefy a gas it must be cooled below its critical temperature. A gas can be liquefied by cooling into below its boiling at given pressure. But this type of technique is not possible for the liquefaction of gases like N2 and O2 which possess very low boiling points. To liquefy such type of gases a special technique based on intermolecular forces is to be used.
If we reduce the velocities of molecules to lower values then the neighboring molecules attract each other, get cooled and condense to a liquid . In order to cause this , the gas is allowed to expand into available volume without supplying any heat from outside. In this process the attractions between the neighboring molecules will be lessened. In doing so, the gas molecules convert some of their kinetic energy into potential energy and travel slowly. As a result of which the average velocity decreases and therefore the temperature of the gas decreases and the gas cools down. In order to cause this, the gas is allowed to expand through a narrow opening called throttle. This way of cooling of low pressure is called Joule-Thomson effect. If the process is repeated several times by allowing the cooled gas again to mix up with the remaining gas by recirculation, finally the molecules get cooled to such a low temperature, and as a result of which the gas condense to a liquid.