Diffusion‐controlled chemical reactions

Transformation are obtained which reduce the system of differential equations for certain types of diffusion‐controlled reactions to the equation for pure diffusion. Simple relationships between the diffusion rate with and without reactions are presented for reversible unimolecular reactions, certain types of reversible bimolecular reactions, and irreversible reactions between species with equal diffusivities. It is shown that these relationships are independent of geometry, hydrodynamics, or boundary conditions, and so the mass transfer coefficient in the presence of reactions can be obtained from the coefficient in the absence of reactions without an explicit knowledge of the mass transfer mechanism. The reaction factor for irreversible reactions with equal diffusivities, obtained by others for specific mass transfer mechanisms, is found to be quite general and essentially independent of the mechanism. Some data on the absorption of sulfur dioxide in a laminar water jet is considered.