Standard Gibbs free energy, enthalpy, and entropy changes as a function of pH and pMg for several reactions involving adenosine phosphates.

The values of these thermodynamic quantities are presented by means of contour diagrams for the range pH 4 to 10 and pMg 1 to 7. These diagrams make the general features of the pH and pMg dependences readily discernible and summarize the results of some 2500 calculations per diagram. There are significant changes in the heat evolved by these reactions over this range of the independent variables. Equations are derived which make it possible to calculate the standard entropy of reaction AS& from the entropy change of the reaction written in terms of particular ionic species, entropy changes of the various acid and metal ion dissociation reactions, the entropies of mixing of the various forms of each reactant and product, and the entropies of dilution of H+ and Mg2+. The relative contributions of enthalpy and entropy to the equilibrium constants of these reactions may be accessed from the diagrams as a function of pH and pMg.