Differentiate between molecularity and order reaction

• Molecularity refers to the number of reactant molecules that must collide simultaneously for a chemical reaction to occur. It is a theoretical concept that applies only to elementary reactions (reactions that occur in a single step). Molecularity can only be an integer value (1, 2, or 3) and cannot be zero or fractional.

• Order of reaction, on the other hand, is an experimentally determined quantity that describes how the rate of a reaction depends on the concentration of reactants. It is the sum of the exponents of the concentration terms in the rate law. The order of reaction can be zero, integer, or fractional.

Here's a table summarizing the key differences:

Feature	Molecularity	Order of Reaction
Definition	Number of colliding molecules in an elementary step	Sum of exponents in the rate law
Determination	Theoretical (based on reaction mechanism)	Experimental
Value	Integer (1, 2, or 3)	Zero, integer, or fractional
Applicability	Elementary reactions only	All reactions (elementary and complex)