Professional Reference Shelf

Solution

The relative velocity is

Calculate the ratio (k_B/_AB) (Let   _AB)

Calculate the relative velocity

Calculate the frequency factor A

The value reported in Masel^† from Wesley is

Close, but no cigar as Groucho Marx would say.

For many simple reaction molecules the calculated frequency factor, A_calc is in good agreement with experiment. For other reactions, A_calc, can be an order of magnitude too high or too low. In general, collision theory tends to over predict the frequency factor A

There are a couple of things that are troublesome about the rate of reaction given by Equation (10), i.e.

First and most obvious is the temperature dependence. A is proportional to the square root of temperature and so therefore is –r_A, i.e.

However we know that the temperature dependence of the rate of chemical reaction on temperature is given by the Arrhenius equation

or

(12)