The correct statements for the activation energy of a reaction are:
(A) Activation energy is the energy difference between the activated complex and the total energy of the reactants.
(B) Higher is the activation energy, the faster is the rate of reaction.
(C) Catalyst increases the rate of the reaction by following the path of lower activation energy.
(D) In the Arrhenius equation, \( E_a \) corresponds to the activation energy
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (C) and (D) only
Reactants must pass through a high-energy activated complex before they become products. The extra energy needed to reach it from the reactants is the activation energy, \( E_\mathrm{a} \). It enters the Arrhenius equation, where a larger \( E_\mathrm{a} \) means a smaller rate constant:
\( \displaystyle k = A\,e^{-E_\mathrm{a}/RT} \)
(A) Activation energy is the energy difference between the activated complex and the total energy of the reactants. — Correct. \( E_\mathrm{a} \) = energy of the activated complex − energy of the reactants.
(B) Higher is the activation energy, the faster is the rate of reaction. — Incorrect. A higher barrier means a smaller fraction of molecules with enough energy (\( e^{-E_\mathrm{a}/RT} \) is smaller), so the reaction is slower.
(C) Catalyst increases the rate of the reaction by following the path of lower activation energy. — Correct. A catalyst provides an alternative pathway with a lower energy barrier, so more molecules can react.
(D) In the Arrhenius equation, \( E_a \) corresponds to the activation energy — Correct. In \( k = A\,e^{-E_\mathrm{a}/RT} \), \( E_\mathrm{a} \) is the activation energy in J mol−1.
NCERT (2026-27 edition):
Temperature Dependence of the Rate of a Reaction – “… \( k = A\,e^{-E_a/RT} \) where A is the Arrhenius factor or the frequency factor. It is also called pre-exponential factor. It is a constant specific to a particular reaction. R is gas constant and Ea is activation energy measured in joules/mole (J mol–1). … The energy required to form this intermediate, called activated complex (C), is known as activation energy (Ea).”
Effect of Catalyst – “… 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.”
