Question
Chemistry Question on Surface Chemistry
The correct statement(s) pertaining to the adsorption of a gas on a solid surface is (are)
Adsorption is always exothermic
Physisorption may transform into chemisorption at high temperature
Physisorption increases with increasing temperature but chemisorption decreases with increasing temperature
Chemisorption is more exothermic than physisorption. however it is very slow due to higher energy of activation
Chemisorption is more exothermic than physisorption. however it is very slow due to higher energy of activation
Solution
(a) In the process of adsoiption, a bond is formed between adsorbate and adsorbent, hence always exothermic.
(b) Physisorption require very low activation energy while chemisorption require 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. electrostatic attraction. In chemisorption, strong chemical bond binds the adsorbate to the adsorbent. Therefore, chemisorption is more exothermic than physical adsorption.