Mesoscopic Description Along the Reaction Coordinate

For so-called ideal systems the chemical potential can be written as 

On the mesoscopic scale the flux-force relation becomes, following Onsager  

Following Kramers analysis we now use reaction rate / that is to a good approximation proportional to the density and introduce the following constant 

Substituting eq 14.58 into eq 14.57, using eq 14.55 and the fact that r is constant, we can integrate eq 14.57 and obtain 

Equation 14.59 is the law of mass action, (discussed by de Groot and Mazur [pages 226 to 232]). The expression for the entropy production, eq 14.56, is also valid when the rate is given by the law of mass action. 

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