Why cannot the molecularity of an elementary chemical reaction ever be zero or a fractional number?

Answer and explanation

Correct answer: C. Molecularity is the physical count of discrete reacting species colliding simultaneously in one step

  1. Step 1: Molecularity is defined as the number of reacting species (atoms, ions, or molecules) that participate in simultaneous collision to bring about a chemical transformation in an elementary step.
  2. Step 2: One cannot have zero molecules colliding, nor can a fraction of a molecule undergo a collision.
  3. Step 3: Therefore, molecularity is strictly a theoretical whole-number integer (1 = unimolecular, 2 = bimolecular, 3 = termolecular).
  4. Step 4: In contrast, the order of a reaction is an empirical quantity derived from rate measurements and can be zero, fractional, or negative.
Answer
Because molecularity represents the actual physical count of discrete reacting atoms, ions, or molecules that collide simultaneously in an elementary step
Why not the others: 'Because reaction rates cannot be measured at zero concentration' confuses molecularity with concentration measurement limits; 'Because catalysts destroy fractional molecules...' is scientifically fabricated; 'Because the Boltzmann constant is an integer' is false (Boltzmann constant is not an integer).

Practise more Chemical Kinetics.

Free questions with an explanation for every one, and full timed NEET UG mock tests.

All Chemical Kinetics questionsTake a mock test

More Chemical Kinetics questions