IIT-JEE 2011 · Paper 1 · Chemistry Q9

ChemistryMultiple correct+4Question 9 of 69

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.

Answer and worked solution

Official answer: A, B, D

(A) Adsorption lowers the gas's entropy, so for spontaneity it must be exothermic. True.
(B) Physisorption at low temperature can turn into chemisorption when heated enough to overcome the activation energy. True.
(C) Physisorption decreases with temperature; chemisorption first increases. False.
(D) Chemisorption has the larger enthalpy (chemical bonds) and an activation barrier, so it is slower. True.

(A), (B), (D)

Topics:Adsorption

IIT-JEE 2011 · Paper 1, Chemistry question 9