What is second order reaction?

A second-order reaction is a chemical reaction in which the rate is proportional to the square of the concentration of one reactant or to the product of the concentrations of two different reactants. The rate equation for a second-order reaction is expressed as Rate, r = k[A]², or r = k[A][B], where ‘k’ is the rate constant, and ‘[A]’ and ‘[B]’ are the concentrations of the respective reactants. The reaction rate increases exponentially with the increase in reactant concentration. Common examples of second-order reactions include certain chemical reactions involving two reactants or the decomposition of a single reactant.