Question

Which among the following is true for chemisorption?

• A. Heat of adsorption is in the range of 20 - 40 $\mathrm{kJ\ mol}^{-1}$.
• B. It is multimolecular layered.
• C. van der Waals forces are involved.
• D. It is favoured at high temperature up to certain limit.

Hint:

Think of chemisorption as a real chemical reaction taking place on a surface. Just like most chemical reactions need heat to overcome an activation energy barrier to get started, chemisorption requires higher initial temperatures than physical adsorption to proceed effectively!

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
Identify the correct characteristic of chemisorption from the given options.

Step 2: Key Formula or Approach:
Chemisorption involves actual chemical bond formation (covalent/ionic) between adsorbate and surface, unlike physisorption which relies on weak van der Waals forces.

Step 3: Detailed Explanation:
(A) 20-40 kJ/mol heat is typical of physisorption; chemisorption requires 80-240 kJ/mol. (B) Multimolecular layers occur only in physisorption; chemisorption is strictly monolayer. (C) van der Waals forces drive physisorption, not chemisorption. (D) Chemisorption needs activation energy, so higher temperatures initially favor it, though extreme heat eventually causes desorption—this is correct.

Step 4: Final Answer:
Chemisorption is favored at high temperatures up to a limit, matching option (D).