Q8 / 69 · JEE Advanced 2011 (Paper 1) · Chemistry
The correct statement(s) pertaining to the adsorption of a gas on a solid surface is(are)
- Correct answerAAdsorption is always exothermic
- Correct answerBPhysisorption may transform into chemisorption at high temperature
- CPhysisorption increases with increasing temperature but chemisorption decreases with increasing temperature
- Correct answerDChemisorption is more exothermic than physisorption, however it is very slow due to higher energy of activation
Solution
(a) In the process of adsorption, 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.
(d) In physical adsorption, van der Waals' force hold the adsorbate and adsorbent together which is a weak electrostatic attraction. In chemisorption, strong chemical bond binds the adsorbate to the adsorbent. Therefore, chemisorption is more exothermic than physical adsorption.
Hence, the correct answer is options: 'A', 'B', 'D'.