Question

Mention any two conditions for liquefying a gas.
What happens to the intermolecular distance during liquefaction of a gas?

Answer 1

Hint: Liquification of gas can be defined as the conversion of gas into liquid phase as the intermolecular force of attraction increases in such a way that the molecules come together and combine to form a liquid state. This can be achieved by either cooling it or compressing it.

Complete step by step answer:
Many gases can be converted into liquid by just cooling them which results in phase transition. Liquefaction is also utilized for analysing the fundamental properties such as intermolecular forces.
(A)We can define a liquified gas as a gas which is converted into liquid from by either compressing or cooling it. We can liquify gases by two conditions. These are: by lowering the temperature and by applying high pressure.
By lowering the temperature, we mean that we are simply converting gases into liquid by cooling the gas molecules. At very low temperatures, the kinetic energy of molecules decreases and gases are converted into liquids.
By applying high pressure, we mean that we are compressing the gas so that the intermolecular distance between the molecules of gas decreases and they come so close to each other such that it will condense into a liquid.
Hence, these are the two conditions for liquefying a gas.

(B)In gases, the interatomic distance between the gas molecule is very large but it decreases when we apply pressure and the gas converts into liquid. The critical temperature is that temperature above which a gas cannot be liquified irrespective of the pressure applied. Above the critical temperature, the kinetic energy of the gas molecules increases as the kinetic energy of the gas increases.
And below the critical temperature, on applying pressure the gas increases the gas molecules will come closer and the attractive force acts upon the molecule so the liquefaction occurs.

Note:
The temperature at which a gas must be cooled before it liquifies by compression process is known as Inversion temperature. This can only be done at inversion temperature because compression releases heat so that it can be cooled. If we reverse the process i.e. decrease the pressure and increase in temperature, it can revert back to the original.