Order of Reactions
Chemical reactions are often classified as zero-order, first-order, second-order, mixed-order, or higher-order. The general reaction aA + bB → cC + dD will be used in the following discussion.
First, the meanings of these orders are defined in terms of initial rate of reaction effect:
Zero-order in the reactant—there is no effect on the initial rate of reaction
First-order in the reactant—the initial rate of reaction doubles when the reactant is doubled
Second order in the reactant—the initial rate of the reaction quadruples when the reactant is doubled
Third order in the reactant—the initial rate of reaction increases eightfold when the reactant is doubled