- Pre-exponential factor
chemical kinetics, the preexponential factor or A factor is the pre-exponential constant in the Arrhenius equation, an empirical relationship between temperature and rate coefficient. It is usually designated by A when determined from experiment, while Z is usually left for collision frequency.
For a first order reaction it has units of s-1, for that reason it is often called frequency factor.
Values of A for some reactions can be found in here.
[http://www.iupac.org/goldbook/P04811.pdf IUPAC Goldbook definition of preexponential factor]
[http://goldbook.iupac.org/P04811.html IUPAC Gold Book definition of pre-exponential factor]
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