The Velocity Coefficient for Bimolecular Reactions in Solution

Abstract

IN a paper of the above title, in the January Journal of the Chemical Society, Norrish and Smith have attempted to find a relation between second-order velocity coefficients for reactions between organic molecules in solution and the temperature coefficients of the reaction rates. As is well known, Hinshelwood has found that for second order gas reactions the rate of reaction can be found by multiplying the number of collisions between reactant molecules by a term e^-E/RT, where E is the experimentally determined energy of activation. Such an expression might arise from any of several mechanisms of activation and reaction. Norrish and Smith have now found that when it is attempted to calculate reaction rates in this same way for reactions in solution, the calculated rates are too large, and that a probability factor, P, must be introduced, which represents the chance of reaction at a collision involving activated molecules. The values found for P in a few reactions range from 4 × 10^-11 to 4.92 × 10^-5. The explanation which they offer for these very small values of P is that simple binary collisions seldom occur, and that a third molecule will often remove a portion of the energy and thus cause deactivation.