Question

Chemisorptions is ____ while physical adsorption is ____ in nature.
(A) Reversible, reversible
(B) Irreversible, reversible
(C) Reversible, irreversible
(D) Irreversible, irreversible

Answer 1

Hint: Adsorption is a surface phenomenon, where an accumulation of molecular species at the surface rather than in the liquid or solid. There are two types of absorption when gas is adsorbed on a solid surface. In this case, gas is adsorbate and solid is adsorbent at which material adsorbs on the surface.

Complete step by step answer:
There are two types of classification of adsorption of gases on solids.
(1) If gas accumulation on the surface of a solid occurs due to weak van der Waals forces, the adsorption is termed as physical adsorption or physisorption.
(2) If gas molecules are held to the surface by chemical bonds, the adsorption is termed as chemical adsorption or chemisorption. The chemical bonds may be ionic or covalent. This adsorption involves a high energy activation which is often referred to as activated adsorption.
These two processes occur simultaneously as the temperature increases may pass into physical adsorption passed into chemical adsorption.
An important characteristic of physical adsorption is reversible.
\[Solid+Gas\rightleftharpoons Gas/Solid+heat\]

Thus, according to Le-chateliers’s principle, more gas adsorbs when pressure is increased as the volume of gas and gas can be removed by decreasing pressure. The physical adsorption is inversely proportional to temperature since this adsorption is exothermic.
Similarly, an irreversible process is a characteristic of chemical adsorption. Since this adsorption is also an exothermic process, but the process is very slow, requiring high energy of activation and high pressure also favorable for chemisorptions.
So, Chemisorptions are irreversible while physical adsorption is reversible.
So, the correct answer is “Option B”.

Note: Lack of specificity, nature, and surface area of adsorbent, enthalpy of adsorption is also the important characteristics of physisorption. Likewise, high specificity, the surface area of adsorbent, and enthalpy of adsorption are the important properties of chemisorptions.