Question

Which of the following is incorrect regarding physisorption?
(A) It occurs because of Van der Waals' forces.
(B) More easily liquefiable gases are adsorbed readily.
(C) Under high pressure, it results in a multi molecular layer on absorbent surfaces.
(D) Enthalpy of adsorption(\[\Delta {{H}_{adsorption}}\]) is low and positive.

Answer 1

Hint: Try to get a rough idea about the process adsorption explained in the surface chemistry chapter. The word physisorption can be split into two words namely, physical and adsorption. Understand the characteristics and distinct features of physical adsorption. Identify the type of forces prevalent in case of physical adsorption.

Complete answer:
Physisorption, also called physical adsorption, is a process in which the electronic structure of the molecule/atom is attached upon adsorption.
The main interacting force in physical adsorption is the Van der Waals force. Although the interacting force is very weak, it plays a crucial role in nature.
Due to weak forces being present, it is observed that easily liquefiable gases are readily adsorbed on the surface of adsorbent.
When sufficient pressure is applied, it is seen that the layer of adsorbent adsorbs multiple layers of attacking particles called adsorbate.
The enthalpy of adsorption is low and negative in polarity. The value varies between -20 to -40 kJ/mol.
From the above statements, we can conclude that the incorrect statement from the given options is enthalpy of adsorption is low and positive.

Therefore, the correct answer is option (D).

Note:
It is important to know that physical adsorption does not involve the formation of new bonds and structure and is thus a reversible reaction. On the other hand, chemical adsorption involves the formation of new bonds and is this termed as an irreversible process as the original compounds cannot be obtained.