A second order reaction is a chemical reaction in which the rate of reaction is proportional to the concentration of each of two reacting molecules
A second order reaction is a reaction whose rate of reaction is determined by the concentration of two chemical species.
A second order reaction is the term describing the reaction rate of a chemical reaction in which the rate is proportional to the product of the concentrations (in moles) of two of the reactants (also called bimolecular kinetics), or to the square of the molar concentration of the reactant if there is only one. Such a reaction might have an equation like rate = k[A][B] or rate = k[A]2, where k is the reaction rate constant, [A] is the concentration of reactant A, and [B] is the concentration of reactant B.Many important biological reactions, such as the formation of double-stranded DNA from two complementary strands, can be described using second order kinetics. In a second-order reaction, the sum of the exponents in the rate law is equal to two. The two most common forms of second-order reactions will be discussed in detail in this section.