Because the functional form of the Eyring and Arrhenius equations are similar, it is tempting to relate the activation parameters with the activation energy and pre-exponential factors of the Arrhenius treatment. However, the Arrhenius equation was derived from experimental data and models the macroscopic rate using only two parameters, irrespective of the number of transition states in a mechanism. In contrast, activation parameters can be found for every transition state of a multistep mechanism, at least in principle. Thus, although the enthalpy of activation, Δ"H"‡, is often equated with Arrhenius's activation energy "E"a, they are not equivalent. For a condensed-phase (e.g., solution-phase) or unimolecular gas-phase reaction step, "E"a = Δ"H"‡ + "RT". For other gas-phase reactions, "E"a = Δ"H"‡ + (1 − Δ"n"‡)"RT", where Δ"n"‡ is the change in the number of molecules on forming the transition state. (Thus, for a bimolecular gas-phase process, "E"a = Δ"H"‡ + 2"RT.")