Semi‐Empirical Calculations of Activation Energies

The predictions of the Eyring semi‐empirical scheme for calculating activation energies are compared with the existing experimental data. It is found that in most cases this agreement is satisfactory. However, the experimental data are not sufficiently accurate to make this scheme appear unique. The experimental activation energies seem to be functions only of the binding energies and do not depend in an important way on either the size of the atoms or on the diatomic force constants. If the reaction a+bc→ab+c is exothermic, it is found that the activation energy is 0.055D′bc, where D′bc is the energy of the bond bc. This formula is derived from the semi‐empirical scheme on the assumption that the attraction between the distant atoms a and c is zero. For exothermic four atom reactions ab+cd→ac+bd, it is found that the activation energy is 0.28(D′ab+D′cd). The numerical factor was adjusted to fit the H2+I2 reaction and although, in most cases, this gives activation energies in agreement with the semiempiri...