Question 58

The number of statement/s which are the characteristics of physisorption is _____.
A. It is highly specific in nature
B. Enthalpy of adsorption is high
C. It decreases with increase in temperature
D. It results into unimolecular layer
E. No activation energy is needed

Correct Answer: 2

A. It is highly specific in nature (False)

Explanation: Physisorption is not specific in nature. Any gas can be adsorbed on the surface of a solid to some extent because the forces involved are weak, universal van der Waals forces. (Chemisorption is highly specific).

B. Enthalpy of adsorption is high (False)

Explanation: Physisorption is a weak physical process with a low enthalpy of adsorption (usually in the range of $$20\text{-}40\text{ kJ/mol}$$). (Chemisorption has a high enthalpy of adsorption, $$80\text{-}240\text{ kJ/mol}$$).

C. It decreases with increase in temperature (True)

Explanation: Adsorption is an exothermic process. According to Le Chatelier's principle, physisorption decreases with an increase in temperature (low temperature is favorable).

D. It results into unimolecular layer (False)

Explanation: Under high pressure, physisorption can result in a multimolecular layer due to the weak van der Waals forces extending beyond the first layer. (Chemisorption results in a unimolecular layer).

E. No activation energy is needed (True)

Explanation: Since physisorption involves only weak physical attraction and no chemical bond formation, it requires no appreciable activation energy.

Hence, Correct answer is 2

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