Question.1: Write down principle of liquefaction of gas.
Ans.: There exists intramolecular force in real gases. So by decreasing the kinetic energy or by increasing the intermolecular force of gas molecules, gases could be liquefied. This could be done in the following two ways:
a. By applying pressure: At high pressure, the volume of gas decreases. As a result, the molecules come closer to each other. Therefore the intermolecular force of gas molecules increases. If this force is too high, then the gas becomes liquid.
b. By decreasing temperature: Sometimes by applying pressure only gases cannot be converted to liquid. At the same time the temperature of the gas has to be decreased below to critical temperature. According to the kinetic theory of gases, if the temperature is decreased, the kinetic energy of the gas molecules also decreases. As a result the volume of the gases decreases. At this stage the intermolecular force of molecules becomes so high that the gases are converted to liquid.
Question.2: Write down the role of critical temperature in liquefaction of gases.
Ans: The temperature above which, a gas can not be liquefied by applying high pressure, but the temperature at which or below which a gas could be liquefied by applying pressure only is called the critical temperature of gas. The critical temperature of CO2 is 31.4°C.
Example: Applying pressure only above 31.4°C CO2 gas does not liquefy. But keeping the temperature below 31.4°C, CO2 could be liquefied by applying pressure only. Therefore, 31.4°C is the critical temperature of CO2.
So, if we want to liquefy any gas, the temperature of that gas should be bellow critical temperature.