Order of Reaction

Let there be a reaction  m1A + m2B à products.

Now, if on the basis of experiment, we find that

R ∝ [A]p [B]​q ​

Where p may or may not be equal to m, and similarly q may or may not be equal to m2.

P is order of reaction with respect to reactant A and q is order of reaction with respect to reactant B and (p+q) is overall order of the reaction.

Note: Order of a reaction can be ‘zero’ or any whole number. It can be fractional number and it can even be negative with respect to a particular reactant. But overall order is not found to be negative for any reaction till observed.

Examples showing different values of order of reactions:

The reaction (ii) does not takes place in the single step. It is almost impossible for all the 12 molecules of the reactants to be in a state of encounter simultaneously. Such a reaction is called complex reaction and talks places in sequence of a number of elementary reactions. For an elementary reaction the sum of stoichiometric coefficients = order of the reactions. But the complex reactions order is to be experimentally calculated.