The correct statement(s) pertaining to the adsorption of a gas on a solid surface is(are)
(i) adsorption is always exothermic
(ii) physisorption may transform into chemsisorption transform into chemisorption at high temperature
(iii) physisorption increases with increasing temperature but chemisorption decreases with increasing temperature .
(iv) chemisorption is more exothermic than physisorption , however it is very slow due to higher energy of activation.

Options

A. Adsorption is always exothermic
B. Physisorption may transform into chemisorption at high temperature
C. Physisorption increases with increasing temperature but chemisorption decreases with increasing temperature
D. Chemisorption is more exothermic than physisorption, however it is very slow due to higher energy of activation

Explanation

(a)In the process of adsorption, a bond is formed between adsorbate and adsorbent, hence always
(b) Physisorption required very low activation energy while chemisorption required high activation energy. Therefore a physisorption may transform into chemisorption but only at high temperature.
(c ) It is wrong statement as at higher temperature, physically adsorbed substance starts desorbing.
(d) In physical adsorption, van der Waal’s force hold the adsorbate and adsorbent together which is a weak electrostatic attraction. In chemisorption, wrong chemical bond binds the adsorbate to the adsorbent. Therefore, chemisorption is more exothermic than physical adsorption.