Question

Which of the following gas molecules has the maximum value of enthalpy of physisorption in a gas mask?

• A. $C_2{H}_6$
• B. $N_2$
• C. $H_{2}O$
• D. $H_2$

Answer 1

The correct option is C $H_{2}O$

Gases	$C_2{H}_6$	$N_2$	$H_{2}O$	$H_2$
Critical temperature (K)	305	126	647	33

The amount of heat that gets evolved when one mole of the adsorbate is adsorbed on adsorbent is known as $Enthalpyofphysisorption$.

Easily liquefiable gas have maximum value of enthalpy of physisorption.

A gas can be liquefied when its temperature is below critical temperature by cooling or compressing.

Critical temperature signifies the force of attraction between the molecules, higher the critical temperature, higher is the inter molecular force of attraction and easier is the liquefication of the gas.

Gases which have high critical temperature ( like $C{l}_2,N{H}_3,C{O}_2,S{O}_2$, etc) are easily liquefiable by appplying pressure alone.

Elemental gases( such as $H_2,N_2,O_2$, etc) cannot be liquefied easily.

From above table it can be concluded that $H_{2}O$ is easily liquefiable. Therefore it will have maximum value of enthalpy of physisorption.

Hence the correct option is (C).