For a bimolecular elementary reaction between A and B, the rate of reaction is expressed as
\( rate=P.Z_{AB}e^{(-\frac{E_a}{RT})} \)
Identify the terms \( P, Z_{AB} \) and \( E_a \) involved in this expression, respectively
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Probability factor, collision frequency, Activation energy
In the collision theory, \( Z_{AB} \) is the collision frequency, \( E_a \) the activation energy, and P the probability (steric) factor that allows for the orientation of the colliding molecules.
Why the other options are incorrect
Option (1) Probability factor, collision number, Absolute energy — Incorrect. \( Z_{AB} \) is a rate of collisions (per second per unit volume), not just a number, and there is no “absolute energy” in the expression.
Option (2) Pressure, collision number, Activation energy — Incorrect. P here is the probability (steric) factor, not pressure.
Option (4) Pressure, collision frequency, Absolute energy — Incorrect. Both P and \( E_a \) are misnamed: they are the probability factor and the activation energy.
NCERT (2026-27 edition):
Collision Theory of Chemical Reactions – …
