Question

What type of forces are operative in (a) physical adsorption and (b) chemical adsorption? Justify the specificity of the two types of adsorption in the light of these forces.

Answer 1

(a) Physical adsorption involves weak van der Waals’ forces. These are non-specific, allowing any gas to be adsorbed on the surface. It forms multiple layers and is usually reversible.

(b) Chemical adsorption involves strong, specific chemical bonds (such as covalent or ionic). It usually forms a monolayer and is mostly irreversible.

Justification: The specificity of chemical adsorption arises because chemical bond formation requires a suitable interaction between the adsorbate and adsorbent. In contrast, the van der Waals’ forces in physical adsorption are general and do not depend on chemical compatibility.