Arrhenius Equation

As per the book (Nivaldo J. Tro)

The Frequency Factor: The number of approaches to the activation barrier per unit time.

The Exponential factor: Number between 0 and 1 that represents the fraction of molecules that have enough energy to make it over the activation barrier on a given approach. The exponential factor is the fraction of approaches that are actually successful and result in the product.

Orientation Factor

Collision Frequency: It is the number of collisions that occurs per unit time.

Orientation Factor: Usually between 0 and 1, which represents the fraction of collisions with an orientation that allows the reaction to occur

I am unable to distinguish the between the exponential factor and orientation factor. Aren't they saying the same thing? How do they differ from each other?

Another doubt is what does the number of approaches mean? i.e. number of approaches taken by a single reactant per sec, or all reactant per sec.


The orientation factor is really an empirical add-on fix as way of trying to make the Arrhenius equation seem more reasonable. Most collisions between molecules do not lead to reaction, which is why the activation energy is there, but even when a molecule has obtained enough energy to react ( by random collisions in solution or vapour) we may know from its structure that it can only react from one side or at one end, then an orientation factor is added.


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