CBSE · Class 12 · Chemistry · Chemical KineticsWhat is meant by the 'order of a reaction'? Differentiate clearly between the order of a reaction and the molecularity of a reaction.

The order of a reaction is defined as the sum of the powers of the concentrations of the reactants in the rate law expression of a chemical reaction. It is an experimentally determined quantity and can be zero, fractional, or integer values. \nDifferences between Order of a Reaction and Molecularity:

1. Definition: Order is the sum of exponents of concentration terms in the rate law equation, whereas molecularity is the total number of reacting species (atoms, ions, or molecules) colliding simultaneously in an elementary step to bring about a chemical reaction.
2. Determination: Order is an experimental quantity determined from the rate law, whereas molecularity is a theoretical concept determined by counting the reacting particles in an elementary reaction.
3. Values: Order can be zero, a fraction, or a whole number, and can even be negative in some complex reactions. Molecularity can only be an integer (1, 2, or 3) and cannot be zero, fractional, or negative.
4. Applicability: Order is applicable to both elementary and complex reactions, whereas molecularity is meaningful only for elementary reactions.