Experimentally, it can be determined that the equilibrium step (equation (2)) is fast, while equation (3) is the rate determining step. The rate of the overall equation is
However, nitrous dioxide is a short-lived intermediate. Because the concentrations of such intermediates are difficult to measure in practice, their concentrations must be expressed in terms of non-intermediates in the rate law. The concentration of can be found by rearranging the equilibrium reaction of the first step and then substituting into equation (4).
