Hydrogen ions transformed thermodynamic properties

When the pH is specified, we enter into a whole new world of thermodynamics because there is a complete set of new thermodynamic properties, called transformed properties, new fundamental equations, new Maxwell equations, new Gibbs-Helmholtz equations, and a new Gibbs-Duhem equation. These new equations are similar to those in chemical thermodynamics, which were discussed in the preceding chapter, but they deal with properties of reactants (sums of species) rather than species. The fundamental equations for transformed thermodynamic potentials include additional terms for hydrogen ions, and perhaps metal ions. The transformed thermodynamic properties of reactants in biochemical reactions are connected with the thermodynamic properties of species in chemical reactions by equations given here. 

This reaction is spontaneous mainly because of the change in the transformed entropy. Note the entropy increases because is produced. For most of these reactions, the enthalpy change at pH 7 determines whether the reaction goes to the right or the left, but sometimes the entropy change does, especially when hydrogen ions are produced by the reaction. Standard transformed thermodynamic properties are given for more enzyme-catalyzed reactions in Chapter 13. 

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