In the arrhenius equation, #k = Ae^(-E_a"/"RT)#, what is the frequency factor?

1 Answer
Apr 30, 2016

In collision theory, a major proposition is that a successful collision (overcoming the activation energy #E_a#) gives you a successful reaction.

The frequency factor is #A#, also known as the pre-exponential factor. This is essentially an experimentally-acquired constant.

It generally represents the frequency of collisions between molecules in a reaction. It is the fraction of molecules that would react if there existed no energy barrier. Here's why.

The Arrhenius equation is:

#\mathbf(k = Ae^(-E_a"/"RT))#

But if there were no energy threshold, above which the reaction can occur, then the activation energy #E_a = 0#.

Thus, #e^(-E_a"/"RT) = e^0 = 1#, and:

#color(green)(k = A)#

So, the higher #A# is for a specific reaction, the more frequent collisions would be observed for that reaction, and thus we would see the reaction successfully occur more easily.

NOTE: Although #A# is temperature-dependent, if we choose a small-enough temperature range, we can assume that #A# is constant for two reactions at different temperatures.