Coupling reaction, entropy generation

If the reactions are independent, each term in the sum must be positive. However, if the reactions are coupled, most simply by having reactants and products in common, only the total entropy generation must be positive. Thus, as is well known in biochemical systems, it is possible for reactions with negative affinity (positive free-energy change) to be driven to products by reactions with positive affinity. 

The concepts discussed in Section 25-9 are applied to binary mixtures of A and B with chemical reaction. Now, the Curie restriction states that there are two first-rank tensorial fluxes, —(q — linear laws. Notice that the two fluxes are not simply q and Ja, but — (q — aJa) and —Ja, as dictated by the classical expression for the rate of entropy generation, which is given by equation (25-49) in canonical form. In other words, one must exercise caution in identifying fluxes and forces such that their products correspond to specific terms in the final expression for sq- The linear laws are... 

Reactions 7.10-7.14 may be described as additions of the N atom of the nucleophile on the N atom of the MNO fragment, coupled with deprotonation, as suggested by pH-dependent rate laws with a first-order behavior in complex and nucleophile concentrations, and followed by rapid adduct reorganizations. The negative activation entropies support an associative mechanism in the initial addition step. The adduct reorganizations generate the different gaseous products, N2 and/or N20. Theoretical (DFT) characterizations of the adduct intermediates have been reported,41 as previously detailed for the OH- additions.36... 

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