order of reaction

The order of reaction , in chemical kinetics, with respect to a certain reactant, is defined as the power to which its concentration term in the rate equation is raised .

For example, given a chemical reaction 2A + B → C with a rate equation

r = k[A]²[B]¹

the reaction order with respect to A would be 2 and with respect to B would be 1, the total reaction order would be 2+1=3. It is not necessary that the order of a reaction be a whole number - zero and fractional values of order are possible - but they tend to be integers. Reaction orders can be determined only by experiment. Their knowledge allows conclusions about the reaction mechanism.

The reaction order is not necessarily related to the stoichiometry of the reaction, unless the reaction is elementary. Complex reactions may or may not have reaction orders equal to their stoichiometric coefficients