Question

What is the difference between order and molecularity of reaction ?

Answer 1

Difference between order and molecularity of reaction :

Order of reaction	Molecularity
i) It is the sum of powers to which concentration terms are raised in final rate equation.	It is the number of atoms molecules or ions that are colloiding with each other in a single step.
ii) it is an experimentally determined quantity	It is determined theoretically from balanced chemical equation.
iii) Order of reaction always refers to overall reaction.	Molecularity of overall reaction has no meaning. It always refers to the species participating in a single step.
v) Knowledge of order of reaction helps in predicting the rate law of a reaction.	Knowledge of molecularity helps in predicting the mechanism of reaction.
v) it is whole number, fractional or may be zero. The order of reaction w.r.t a species in reaction may be negative but overall order of reaction is always positive.	It is always a whole number.
vi) order of reactions can be changed by changing physical parameters such as concentration, temperature.	Molecularity is always characteristic for each step and thus cannot be changed.