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

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:

$\setminus m a t h b f \left(k = A {e}^{- {E}_{a} \text{/} R T}\right)$

But if there were no energy threshold, above which the reaction can occur, then the activation energy ${E}_{a} = 0$.

Thus, ${e}^{- {E}_{a} \text{/} R T} = {e}^{0} = 1$, and:

$\textcolor{g r e e n}{k = A}$

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.