Question

Give two differences between order of reaction and molecularity of reaction.

Hint:

Molecularity has no meaning for complex (multi-step) reactions, whereas order applies to both elementary and complex reactions.

Answer 1

1. Definition/Determination: Order is the sum of powers of concentration terms in the experimental rate law; it is an experimental quantity. Molecularity is the number of reacting species colliding simultaneously in an elementary step; it is a theoretical concept.
2. Values: Order can be zero, fractional, or an integer. Molecularity can only be a positive integer (1, 2, 3) and cannot be zero or fractional.