Consider the following statements about the effect of temperature on the rate of a reaction:
(A) In the Arrhenius equation, the activation energy and the Arrhenius factor (A) are taken as constants for a given reaction.
(B) Effective collisions are those in which the colliding molecules have energy equal to or greater than the threshold energy and proper orientation.
(C) As the temperature increases, the fraction of molecules with energy equal to or greater than the activation energy increases.
(D) The rate constant of a reaction depends on temperature.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, B, C and D
The Arrhenius equation, \( k=A\,e^{-E_a/RT} \), describes how the rate constant changes with temperature; the factor \( e^{-E_a/RT} \) is the fraction of molecules with energy greater than Ea.
(A) In the Arrhenius equation, the activation energy and the Arrhenius factor (A) are taken as constants for a given reaction. — True. A is a constant specific to a reaction, and the same Ea is used at both temperatures when the equation is written for T1 and T2; only k changes with T.
(B) Effective collisions are those in which the colliding molecules have energy equal to or greater than the threshold energy and proper orientation. — True. A collision forms products only when it has both enough energy and the proper orientation.
(C) As the temperature increases, the fraction of molecules with energy equal to or greater than the activation energy increases. — True. On heating, the energy distribution curve shifts and spreads to higher energies, so more molecules cross Ea.
(D) The rate constant of a reaction depends on temperature. — True. For a 10° rise in temperature the rate constant is nearly doubled.
NCERT (2026-27 edition):
3.4 Temperature Dependence of the Rate of a Reaction – “It has been found that for a chemical reaction with rise in temperature by 10°, the rate constant is nearly doubled. The temperature dependence of the rate of a chemical reaction can be accurately explained by Arrhenius equation (3.18). …
\( \displaystyle k=A\,e^{-E_a/RT} \qquad (3.18) \)
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).”
“Increasing the temperature of the substance increases the fraction of molecules, which collide with energies greater than Ea. …”
3.5 Collision Theory of Chemical Reactions – “… The collisions in which molecules collide with sufficient kinetic energy (called threshold energy) and proper orientation, so as to facilitate breaking of bonds between reacting species and formation of new bonds to form products are called as effective collisions.”