The decrease in rate of reaction brought about by the addition of a substance inhibitor), by virtue of its effect on the concentration of a reactant, catalyst or reaction intermediate. For example, molecular oxygen and p-benzoquinone can react as 'inhibitors' in many reactions involving radicals as intermediates by virtue of their ability to act as scavengers toward these radicals. If the rate of a reaction in the absence of inhibitor is v 0 and that in the presence of a certain amount of inhibitor is v, the degree of inhibition (i) is given by: \[i=\frac{v_{0}- v}{v_{0}}\]