Question

Distinguish between Order and Molecularity of reaction.

Differentiate between order of a reaction and its molecularity.

How does order of a reaction differ from the molecularity of the reaction?

Give one difference between the order of a reaction and its molecularity.

Answer 1

	Order	Molecularity
i.	It is an experimentally determined property.	It is a theoretical entity.
ii.	It is the sum of the powers of the concentration terms of the reactants that appear in the rate equation.	It is the number of reactant molecules taking part in an elementary reaction.
iii.	It may be an integer, fraction, or zero.	It is an integer.
iv.	It is not based on a balanced chemical equation.	It is based on a balanced chemical equation.

Answer 2

Sr. No.	Order of reaction	Molecularity of reaction
1.	It is the sum of the concentration terms on which the rate of reaction actually depends, or it is the sum of the exponents of the concentrations in the rate law equation.	It is the number of atoms, ions, or molecules that must collide with one another simultaneously so as to result in a chemical reaction.
2.	It need not be a whole number, i.e., it can be fractional as well as zero.	It is always a whole number.
3.	Only experimentation can determine it; calculation is not possible.	You can calculate it by simply adding the molecules from the slowest step.
4.	It is an overall reaction, and no separate steps are written to obtain it.	The overall molecularity of a complex reaction has no significance. It is the only slowest step whose molecularity has significance for the overall reaction.
5.	Even the order of a simple reaction may not be equal to the number of molecules in the reactants, as seen by the unbalanced equation.	Typically, the stoichiometry of the equation provides the molecularity for simple reactions.
6.	It may be an integer, fraction, or zero.	It is always an integer and never a fraction or zero.