In reaction between two phases, two factors a priori determine the overall measured rate of reaction. The first is the rate of chemical reaction at the interface; the second is the rate of transport of reactant, or product of reaction, to or from the interface. For heterogeneous reaction in which one or both phases are fluid, the transport takes place between the interface and the point of measurement.In the present work, dealing with the fluid-fluid or fluid-solid heterogeneous reaction, a quantitative relationship is derived for the measured rate as a function of the chemical reaction rate and rate of physical transport. No arbitrary postulates as to mechanism are made. The results follow in the first place from a solution of the diffusion equation with chemical reaction at the interface constituting one of the boundary conditions. In the second place, diffusion as a mode of transport is generalized to include transport due to stirring or other type of agitation.
THE NERNST THEORYIn 1904, Nernst (21, 2) proposed a theory of heterogeneous reaction , which has been referred to widely. In this theory certain assumptions are made as to the chemical and physical factors of the liquid-solid heterogeneous reaction. On the chemical side, reaction is supposed to be in-