keqG

KeqG is a notation encountered in chemical thermodynamics referring to the equilibrium constant expressed in terms of Gibbs free energy. It is not a universally standardized symbol and may appear in different sources or software to emphasize the thermodynamic basis of chemical equilibrium.

For a reaction with standard Gibbs free energy change ΔG°rxn, KeqG is related by the equation ΔG°rxn = -RT ln KeqG, where R is the gas constant and T is the absolute temperature. Equivalently, KeqG = exp(-ΔG°rxn/RT). KeqG is dimensionless when the standard states are defined by activities (or by the conventional standard-state conventions for solutions and gases).

KeqG is closely related to the conventional equilibrium constant K, Kc, or Kp, but with an emphasis on Gibbs free energy. When standard-state activities are used and dilute solutions apply, KeqG and the traditional equilibrium constants describe the same equilibrium, though the symbols may differ. Differences in standard-state conventions (for example, concentrations versus activities) can lead to numerical differences among KeqG, Kc, and Kp, even though they describe the same underlying reaction.

Calculation and data sources: KeqG can be computed from standard Gibbs energies of formation ΔG°f of reactants and products via ΔG°rxn = ∑ν_i ΔG°f,i, and then KeqG = exp(-ΔG°rxn/RT). It can also be derived from experimental ΔG°rxn values or thermodynamic databases. In practice, keqG is used in contexts stressing Gibbs-energy relationships and in certain databases or software tools.