FACTORS AFFECTING RATE OF REACTION:
The rate of a chemical reaction measures how quickly reactants are consumed or products are formed. It depends on the conditions under which the reaction is carried out.
- Concentration: Generally, an increase in reactant concentration leads to an increase in the reaction rate. This is because a higher concentration provides more reactant particles, leading to a higher collision frequency.
- Temperature: The rate of reaction increases with the increase in temperature. In most cases, the rate of reaction becomes nearly double for 10° rise in temperature.
- Catalysts: Catalysts are substances that accelerate a reaction by providing an alternative reaction pathway with lower activation energy. They increase the rate of reaction without being consumed in the process.
Assertion (A): A catalyst cannot make a non-spontaneous reaction take place.
Reason (R): A catalyst does not alter the Gibbs energy change, ΔG, of a reaction.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A).
A catalyst gives the reaction a new pathway with a lower activation energy, so the reaction becomes faster. Whether a reaction can take place at all is decided by its Gibbs energy change, ΔG: a reaction with a negative ΔG is spontaneous.
Assertion (A): A catalyst cannot make a non-spontaneous reaction take place. — True. A catalyst speeds up only reactions that are spontaneous; it does not catalyse non-spontaneous reactions.
Reason (R): A catalyst does not alter the Gibbs energy change, ΔG, of a reaction. — True. The catalyst lowers the energy barrier, but the reactants and products, and so ΔG, stay the same.
Why R explains A?
Assertion (A) is about which reactions a catalyst can help; Reason (R) is about what a catalyst leaves unchanged.
Since the catalyst does not change ΔG, a reaction that is non-spontaneous (ΔG positive) remains non-spontaneous after the catalyst is added. The catalyst can only make a reaction that is already possible go faster, so R gives the cause of A.
NCERT (2026-27 edition):
3.4.1 Effect of Catalyst – “A small amount of the catalyst can catalyse a large amount of reactants. A catalyst does not alter Gibbs energy, ΔG of a reaction. It catalyses the spontaneous reactions but does not catalyse non-spontaneous reactions.”