Why the Reaction Order of a Bimolecular Reaction Should be 2.33 Instead of 2?

01 December 2022, Version 5
This content is a preprint and has not undergone peer review at the time of posting.


Predicting the reaction kinetics, that is, how fast a reaction can happen in a solution, is essential information for many processes, such as industrial chemical manufacturing, refining, synthesis and separation of petroleum products, environmental processes in air and water, biological reactions in cells, biosensing, and drug delivery. Collision theory was originally developed to explain the reaction kinetics of gas reactions with no dilution. For a reaction in a diluted inert gas solution or a diluted liquid solution, diffusion often dominates the collision process. Thus, it is necessary to include diffusion in such a calculation. Traditionally the classical Smoluchowski rate is used as a starting point to predict the collision frequency of two molecules in a diluted solution. In this report, a different collision model is derived from the adsorption of molecules on a flat surface. A surprising result is obtained showing that the reaction order for biomolecular reaction should be 2 and 1/3 instead of 2, following a fractal reaction kinetics.


collision theory
rate constant
diluted solution


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