Question

Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the particles. Following are the critical temperatures of some gases.

Gases	$H_2$	$He$	$O_2$	$N_2$
Critical temperature $\left(K\right)$	$33.2$	$5.3$	$154.3$	$126$

From the above data what would be the order of liquefaction of these gases? Start writing the order from the gas liquefying first.

• A. $N_2,O_2,He,H_2$
• B. $O_2,N_2,H_2,He$
• C. $H_2,He,O_2,N_2$
• D. $He,O_2,H_2,N_2$

Answer 1

The correct option is B $O_2,N_2,H_2,He$

$\text{Critical temperature}$

Critical temperature (of a substance) can be defined as the highest possible temperature at which the substance can exist as a liquid. At temperatures above the critical temperature, a gas can never be liquified and the critical temperature depends on the strength of intermolecular forces between the molecules, stronger the intermolecular forces, higher will be the critical temperature.

Hence, higher the critical temperature of a gas, more easily the gas will be liquified as molecules will be close enough to get liquified.

Increasing order of critical temperature is:

$He<H_2<N_2<O_2$

So, order of liquefaction of gases will be:

$O_2>N_2>H_2>He$

Hence, option $\left(D\right)$ is the correct answer.