Consider the following statements and select the correct statements:
(A) The energy required to form the activated complex is known as activation energy.
(B) The Arrhenius equation explains the temperature dependence of the rate of chemical reaction.
(C) The number of collisions per second per unit volume of the reaction mixture is known as collision frequency.
(D) Lower the value of activation energy, lower will be the rate of reaction.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only
By collision theory, molecules react only when they collide with enough energy and in the proper orientation. The colliding molecules first form an unstable intermediate, the activated complex; the energy needed to form it is the activation energy, \( E_a \). The Arrhenius equation links the rate constant with \( E_a \) and the temperature:
\( \displaystyle k = A\,e^{-E_a/RT} \)
(A) The energy required to form the activated complex is known as activation energy. — Correct. This is the definition of \( E_a \): the energy difference between the activated complex and the reactant molecules.
(B) The Arrhenius equation explains the temperature dependence of the rate of chemical reaction. — Correct. As T rises, the factor \( e^{-E_a/RT} \) grows, so k and the rate increase.
(C) The number of collisions per second per unit volume of the reaction mixture is known as collision frequency. — Correct. This is the definition of the collision frequency, Z; for a bimolecular reaction, rate \( = Z_{AB}\,e^{-E_a/RT} \).
(D) Lower the value of activation energy, lower will be the rate of reaction. — Incorrect. A lower activation energy gives a higher rate, because \( e^{-E_a/RT} \), the fraction of molecules with enough energy to react, becomes larger. This is how a catalyst speeds up a reaction.
NCERT (2026-27 edition):
Temperature Dependence of the Rate of a Reaction – “… The energy required to form this intermediate, called activated complex (C), is known as activation energy (Ea).”
Collision Theory of Chemical Reactions – “Though Arrhenius equation is applicable under a wide range of circumstances, collision theory, which was developed by Max Trautz and William Lewis in 1916 -18, provides a greater insight into the energetic and mechanistic aspects of reactions. It is based on kinetic theory of gases. According to this theory, the reactant molecules are assumed to be hard spheres and reaction is postulated to occur when molecules collide with each other. The number of collisions per second per unit volume of the reaction mixture is known as collision frequency (Z). Another factor which affects the rate of chemical reactions is activation energy (as we have already studied).”