a concept in chemical kinetics. The order of a reaction is determined as the sum of the exponents n1 and n2 in the equation
r = k [A1]n1[A2]n3
which expresses the dependence of the reaction rate r on the concentrations [A1] and [A2] of the initial materials, where k is the rate constant. Reactions in which n1 + n2 = 1, 2, … are called first-order reactions, second-order reactions, and so on.
