Consider the following statements about catalysts.
(A) MnO2 increases the rate of decomposition of potassium chlorate into potassium chloride and oxygen considerably.
(B) An added substance that reduces the rate of a reaction is called an inhibitor.
(C) According to the intermediate complex theory, a catalyst forms permanent bonds with the reactants.
(D) A catalyst catalyses the non-spontaneous reactions as well as the spontaneous reactions.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (B) only
A catalyst is a substance which increases the rate of a reaction without itself undergoing any permanent chemical change.
(A) MnO2 increases the rate of decomposition of potassium chlorate into potassium chloride and oxygen considerably. — True. MnO2 acts as the catalyst in this decomposition:
\( \displaystyle \ce{2KClO3} \xrightarrow{\ce{MnO2}} \ce{2KCl + 3O2} \)
(B) An added substance that reduces the rate of a reaction is called an inhibitor. — True. The word catalyst is not used for such a substance; it is an inhibitor.
(C) According to the intermediate complex theory, a catalyst forms permanent bonds with the reactants. — False. The catalyst forms temporary bonds with the reactants. The intermediate complex has a transitory existence and decomposes to give the products and the catalyst back.
(D) A catalyst catalyses the non-spontaneous reactions as well as the spontaneous reactions. — False. A catalyst does not alter ΔG of a reaction, so it catalyses only the spontaneous reactions; it does not catalyse non-spontaneous reactions.
NCERT (2026-27 edition):
3.4.1 Effect of Catalyst – “A catalyst is a substance which increases the rate of a reaction without itself undergoing any permanent chemical change. For example, MnO2 catalyses the following reaction so as to increase its rate considerably.”
\( \displaystyle \ce{2KClO3} \xrightarrow{\ce{MnO2}} \ce{2KCl + 3O2} \)
“The word catalyst should not be used when the added substance reduces the rate of raction. The substance is then called inhibitor. The action of the catalyst can be explained by intermediate complex theory. According to this theory, a catalyst participates in a chemical reaction by forming temporary bonds with the reactants resulting in an intermediate complex. This has a transitory existence and decomposes to yield products and the catalyst.”
“…A catalyst does not alter Gibbs energy, ΔG of a reaction. It catalyses the spontaneous reactions but does not catalyse non-spontaneous reactions.”