Which factor in Arrhenius equation, corresponds to fraction of molecules having kinetic energy greater than activation energy ?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → e−Ea/RT
The Arrhenius equation relates the rate constant to the activation energy:
\( \displaystyle k=A\,e^{-E_a/RT} \)
Here A is the frequency (pre-exponential) factor, and the factor e−Ea/RT is the fraction of molecules whose kinetic energy is equal to or greater than Ea, from the Maxwell–Boltzmann distribution. Raising the temperature or lowering Ea increases this fraction and so the rate.
Why the other options are incorrect
Option (1) ln k — Incorrect. It is the logarithm of the rate constant, \( \ln k=\ln A-\frac{E_a}{RT} \), not the fraction of molecules.
Option (2) ln A — Incorrect. It is the intercept of the plot of ln k against 1/T, related to the collision frequency.
Option (3) RT — Incorrect. It is a measure of the average thermal energy per mole, not a fraction.
NCERT (2026-27 edition):
Temperature Dependence of the Rate of a Reaction – …
