The order of a reaction with respect to a reactant is the power to which the concentration of the reactant is raised in the rate equation. If the order is zero with respect to a reactant then the rate is unaffected by a change in the concentration of that reactant.rate α [A]0If the order is one with respect to a reactant then the rate is directly proportional to the concentration of that reactant and the rate doubles when the concentration doubles.rate α [A]1If the order is two with respect to a reactant then the rate is directly proportional to the square of the concentration of that reactant and the rate quadruples when the concentration doubles.rate α [A]2