Consider the following elementary reaction: NO2(g) + O3(g) → NO3(g) + O2(g) Suppose we let k1 stand for the rate constant of this reaction, and k−1 stand for the rate constant of the reverse reaction. Write an expression that gives the equilibrium concentration of O2 in terms of k1, k−1, and the equilibrium concentrations of NO2, O3, and NO3. [O2] =