Kinetics and the Rate Equation 5-1 The rate equation is an experimentally derived equation that explains the relationship between the concentration of reactants and the rate of the reaction. 5-2 Rate = k [A]m[B]n 5-3 Overall order = 1.5 Halogenation of Alkanes 5-4 5-5 5-6 Radical bromination is more selective because of its slightly higher activation energy required to break a C-H bond during the propagation steps (when the bromine radical abstracts a proton from the substrate). Though the difference in activation energy is not huge (Cl = ~1 kcal/mol and Br = ~3 kcal/mol), it leads to a significant difference in selectivity.