Read the Passage carefully and answer the Questions.
Kinetic studies not only help us to determine the rate of a chemical reaction but also describe the conditions by which the reaction rates can be altered. The factors such as concentration, temperature, pressure and catalyst affect the rate of a reaction. The speed of a reaction or the rate of a reaction can be defined as the change in concentration of a reactant or product in unit time.
Rate = \( k [A]^x [B]^y \)
Here k is the rate constant
\( x + y \) gives the overall order of a reaction, whereas x and y represent the order with respect to the reactants A and B, respectively.
Which of the following statements are correct?
(A) Catalysts increase the rate of a chemical reaction.
(B) Catalysts can catalyze both spontaneous and non-spontaneous reactions.
(C) Higher the activation energy for a chemical reaction, lower is the rate of the reaction.
(D) Catalyst increases the potential energy barrier.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) and (C) only
A catalyst provides an alternative path of lower activation energy, so more molecules can cross the energy barrier and the reaction becomes faster. The catalyst does not change the energies of the reactants and products, so it does not change \( \Delta G \) of the reaction. The dependence of the rate constant on activation energy is given by the Arrhenius equation:
\( \displaystyle k = A\,e^{-E_a/RT} \)
(A) Catalysts increase the rate of a chemical reaction. — Correct. Lowering the activation energy increases the rate constant and hence the rate.
(B) Catalysts can catalyze both spontaneous and non-spontaneous reactions. — Incorrect. A catalyst does not alter the Gibbs energy, so it can only speed up a reaction that is already spontaneous; it cannot make a non-spontaneous reaction take place.
(C) Higher the activation energy for a chemical reaction, lower is the rate of the reaction. — Correct. A larger \( E_a \) makes \( e^{-E_a/RT} \) smaller, so a smaller fraction of molecules can react and the rate is lower.
(D) Catalyst increases the potential energy barrier. — Incorrect. A catalyst lowers the potential energy barrier; that is how it speeds up the reaction.
NCERT (2026-27 edition):
Effect of Catalyst – …
