Which of the following best explains the effects of a catalyst on the rate of a reversible reaction?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → It provides a new reaction path with a lower activation energy
A catalyst gives the reaction a different path with a lower activation energy. At the same temperature, a larger fraction of molecules now has enough energy to cross the lower barrier, so the reaction goes faster.
In a reversible reaction it speeds up the forward and backward reactions to the same extent, so equilibrium is reached sooner but does not change.
Why the other options are incorrect
Option (1) It decreases the rate of the reverse reaction — Incorrect. A catalyst speeds up the reverse reaction too, as much as the forward one.
Option (2) It increases the kinetic energy of the reacting molecules — Incorrect. The kinetic energy of the molecules depends on the temperature, which the catalyst does not change. A catalyst lowers the energy barrier instead of raising the energy of the molecules.
Option (3) It moves the equilibrium position to the right — Incorrect. A catalyst does not change the equilibrium constant; it only helps the system reach the same equilibrium faster.
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. … It is believed that the catalyst provides an alternate pathway or reaction mechanism by reducing the activation energy between reactants and products and hence lowering the potential energy barrier as shown in Fig. 3.11. It is clear from Arrhenius equation (3.18) that lower the value of activation energy faster will be the rate of a reaction.”
\( \displaystyle k = A\,e^{-E_a/RT} \qquad (3.18) \)
Fig. 3.11: Effect of catalyst on activation energy