Explain the characteristics of physisorption and chemisorption.

(N/A) Characteristics of Physisorption (Physical Adsorption):
$(i)$ Lack of specificity: $A$ given surface of an adsorbent does not show any preference for a particular gas because van der Waals' forces are universal.
$(ii)$ Nature of adsorbate: Easily liquefiable gases (e.g.,$NH_3$,$HCl$) are adsorbed more readily because van der Waals' forces are stronger near the critical temperature.
$(iii)$ Reversible nature: It is generally reversible. The process is represented as: $\text{Solid} + \text{Gas} \rightleftharpoons \text{Gas/Solid} + \text{Heat}$. Adsorption increases with pressure and decreases with an increase in temperature.
$(iv)$ Surface area: The extent of adsorption increases with an increase in the surface area of the adsorbent.
$(v)$ Enthalpy of adsorption: It is low,typically in the range of $20-40 \ kJ \ mol^{-1}$,due to weak van der Waals' forces.
$(B)$ Characteristics of Chemisorption (Chemical Adsorption):
$(i)$ High specificity: It occurs only if there is a possibility of chemical bond formation between the adsorbent and adsorbate.
$(ii)$ Irreversibility: It is usually irreversible as it involves the formation of chemical compounds.
$(iii)$ Surface area: Like physisorption,it increases with an increase in surface area.
$(iv)$ Enthalpy of adsorption: It is high,typically in the range of $80-240 \ kJ \ mol^{-1}$,due to the formation of strong chemical bonds.
$(v)$ Temperature effect: It often increases with an increase in temperature initially,as it requires activation energy.