Predictability of Reaction Rate from Theory

4 PREDICTABILITY OF REACTION RATE FROM THEORY Concentration-Dependent Term 

Assuming that we already know the mechanism of reaction and whether or not it is elementary, we may then proceed to the prediction of the frequency factor and activation energy terms of the rate constant. 

If we are lucky, frequency factor predictions from either collision or transition-state theory may come within a factor of 100 of the correct value however, in specific cases predictions may be much further off. 

Though activation energies can be estimated from transition-state theory, reliability is poor, and it is probably best to estimate them from the experimental findings for reactions of similar compounds. For example, the activation energies of the following homologous series of reactions 

The frequent order-of-magnitude predictions of the theories tend to confirm the correctness of their representations, help find the form and the energies of various intermediates, and give us a better understanding of chemical structure. However, theoretical predictions rarely match experiment by a factor of two. In addition, we can never tell beforehand whether the predicted rate will be in the order of magnitude of experiment or will be off by a factor of 10. Therefore, for engi- 

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