Editing Arrhenius equation (section)

== Modified Arrhenius equation ==
The modified Arrhenius equation<ref>[http://goldbook.iupac.org/M03963.html IUPAC Goldbook definition of modified Arrhenius equation].</ref> makes explicit the temperature dependence of the pre-exponential factor. The modified equation is usually of the form
<math display="block">k = A T^n e^\frac{- E_\text{a}}{RT}.</math>

The original Arrhenius expression above corresponds to {{nowrap|1=''n'' = 0}}. Fitted rate constants typically lie in the range {{nobr|−1 < ''n'' < 1}}. Theoretical analyses yield various predictions for ''n''. It has been pointed out that "it is not feasible to establish, on the basis of temperature studies of the rate constant, whether the predicted ''T''<sup>1/2</sup> dependence of the pre-exponential factor is observed experimentally".<ref name="Connors"/>{{rp|190}} However, if additional evidence is available, from theory and/or from experiment (such as density dependence), there is no obstacle to incisive tests of the Arrhenius law.

Another common modification is the [[stretched exponential]] form{{citation needed|date=January 2013}}
<math display="block">k = A \exp \left[-\left(\frac{E_a}{RT}\right)^\beta\right],</math>
where ''β'' is a dimensionless number of order 1. This is typically regarded as a purely empirical correction or ''[[fudge factor]]'' to make the model fit the data, but can have theoretical meaning, for example showing the presence of a range of activation energies or in special cases like the Mott [[variable range hopping]].