Given the small temperature range of kinetic studies, it is reasonable to approximate the activation energy as being independent of the temperature. Similarly, under a wide range of practical conditions, the weak temperature dependence of the pre-exponential factor is negligible compared to the temperature dependence of the factor ⁠ e − − E a R T ⁠ ; except in the case of "barrierless" diffusion -limited reactions, in which case the pre-exponential factor is dominant and is directly observable.