Limited Validity of Linear Laws

An interesting case is presented by chemical reactions. For simplicity, we consider an ideal solution in which the molecules M and N participate in the reaction 

Their steady-state concentrations are maintained such that the chemical affinity A, defined by Equation 4.4 (A = pM - gN), is positive and thus the chemical system is out of equilibrium. The reaction velocity uch is positive and given by 

We now derive the relation between the chemical flow rate uch and its driving force A. Earlier we defined 

At equilibrium, the chemical velocity uch is zero and thus v = v. This allows us to write 

The reaction velocity as a function of the chemical affinity. The coordinates are in dimensionless units. 

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