Surface chemistry deals with the phenomenon that occurs at the surfaces or interfaces. The interface or surface is represented by separating the bulk phases by a hyphen or a slash. For example, the interface between a solid and a gas may be represented by solid-gas or solid/gas. Due to complete miscibility, there is no interface between the gases. The bulk phases that we come across in surface chemistry may be pure compounds or solutions. The interface is normally a few molecules thick but its area depends on the size of the particles of bulk phases. Many important phenomena, noticeable amongst these being corrosion, electrode processes, heterogeneous catalysis, dissolution and crystallization occur at interfaces. The subject of surface chemistry finds many applications in industry, analytical work and daily life situations.
The mechanism of heterogeneous catalysis involves the following steps:
A. Occurrence of chemical reaction on the catalyst's surface through formation of an intermediate
B. Diffusion of reaction products away from catalyst's surface
C. Diffusion of reactants on the surface of the catalyst
D. Adsorption of reactant molecules on the surface of the catalyst
E. Desorption of reaction products from the catalysts surface and thereby, making the surface available again for more reaction to occur.
What is the correct sequence of the steps?
Choose the correct answers from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → CDAEB
The modern adsorption theory explains heterogeneous catalysis as five steps in the order in which molecules meet and leave the catalyst surface: the reactants must first reach the surface (C) and be adsorbed (D) before they can react (A); the products are then desorbed (E) and finally diffuse away (B).
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Adsorption Theory of Heterogeneous Catalysis – …
