(2) What is the order of substance A in the rate law?
The data in the table do not give a case where the concentration of B is held constant while the concentration of A is changed. However, the concentrations of both reactants in the third case are three times greater than the concentrations of the reactants in the first case. The rate in the third case is nine times the rate of the first case. Since the reaction is second order in B, tripling the concentration of B would increase the rate by a factor of nine. The reaction must therefore be zero order in A.
