Principles of mass transfer between two phases

When two reactants are present in different phases, at least one of them has to be transported to another phase to meet the other reactant, to make a reaction possible. There are several possibilities, depending on the place where the chemical reaction occurs. We may distinguish three situations  

The transport rates of the reactants generally influence the reaction rates. The transport of a component from one phase into another is determined by two different factors the phase equilibrium and the transport rate coefficients in each of the phases. The phase equilibrium describes the concentration ratio at either side of the interface. For describing these we use the concepts of solubility, volatility Henry coefficient, distribution coefficient, etc.. 

The transport rate of a component that is transferred from one phase to another, is the result of the different transport rates in each phase. Each of these is determined by the difference in die concentrations at the interface and in the bulk of that phase. The transport rate in each phase, relative to the concentration differences, can be described by either a diffusivity or by a mass transfer coefficient, depending on the prevailing transport mechanism. 

The transport of a component in a mixture, with respect to the mixture, is called diffusion if the mixture is stationary. In gases, the mechanism of diffusion is related to the motion of the molecules, which is described by the kinetic gas theory. In liquids and amorphous solids, the mechanism of diffusion is different, since the interaction between the molecules is so much stronger. 

In a flowing fluid (gas or liquid) the transport of matter is the result of the combined effects of diffusion and convection. This is usually called mass transfer. As for diffusion, the rate of mass transfer of a component in a mixture is primarily determined by the concentration difference of that component. The rate constant of mass transfer is determined by the molecular diffusivity of that 

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