Question

Write two main differences between order of reaction and molecularity of a reaction?

Answer 1

Hint: In order to solve this question, you need to recall the concept of chemical kinetics. You should know that it is concerned with understanding the rates of chemical reactions.

Complete step by step answer:
As we know every chemical reaction reacts in a unique way with time, and the ‘speed’ with which the concentrations of the reactants are consumed by the reaction is called the ‘rate of the reaction’ and is usually symbolized with r.

Now, let us differentiate between order and molecularity of a reaction.

Order of a reaction	Molecularity of a reaction
It is the sum of the exponents of the molar concentration(s) in the rate law expression. Order need not be a whole number always. Order can be determined experimentally only.Order cannot be determined by looking at the stoichiometric coefficients.	The number of atoms, ions, molecules that must collide with one another simultaneously to result in a chemical reaction. Molecularity is always a whole number. Molecularity can be calculated directly by looking at the balanced equation.Molecularity can be determined by looking at the stoichiometric coefficients.

Let’s be precise.
Molecularity means the number of concentration terms involved in rate determining step.
Order is the sum of the power of the concentration terms present in rate
determining steps.

Note: Remember that the molecularity cannot be greater than 3, because more than three molecules may not mutually collide or come close in a chemical reaction.