Question

What is the difference between the order of a reaction and the molecularity of a reaction?

Give any four points of difference between the molecularity and order of a reaction.

Answer 1

Order of a reaction	Molecularity of a reaction
The order of a reaction is an experimental quantity. It can be zero and even a fraction	Molecularity of a reaction is the number of species (atoms, ions, or molecules) taking part in the elementary reaction. It cannot be zero or a non-integer.
The order is applicable to elementary as well as complex reactions.	Molecularity is applicable only for elementary reactions.
For complex reactions, the order is given by the slowest step.	The molecularity of the slowest step is equal to the order of the overall reaction.

Answer 2

Sr. No.	Molecularity of a reaction	Order of a reaction
1.	It refers to the quantity of reacting species, atoms, ions, or molecules that collide simultaneously to produce the chemical change.	It is the sum of the powers to which the concentration terms of the reactants are raised in the rate law expression.
2.	It can never have a negative value and only positive integral values, such as 1, 2, 3, etc.	It can be zero, integral, fractional, or even negative.
3.	Molecularity is a theoretical concept, and its value is derived from the mechanism of the reaction.	The rate law of the reaction, which is based on experimental data, is the source of this experimental fact.
4.	It applies to an elementary reaction only (not to complex reactions).	It applies to both elementary and complex reactions and reflects the overall kinetics.