Step-by-step explanation:
The overall rate of a reaction between two species doubles when: the order of both species changes or any of the species changes.
The overall order of the reaction is found by adding up the individual orders. For example, if the reaction is first order with respect to both A and B (a = 1 and b = 1), the overall order is 2. Therefore overall order is 2 or second order reaction although order of individual species is 1.