Prediction of Gibbs energies of formation—I. Relationships among Gibbs energies of formation of hydroxides,oxides and aqueous ions |
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| Authors: | Yves Tardy Robert M Garrels |
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| Institution: | Centre de Sédimentologie, 1 rue Blessig, Strasbourg, France;Department of Geological Sciences, Northwestern University, Evanston, Illinois, U.S.A. |
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| Abstract: | A parameter called ΔO2? is defined as the difference between the Gibbs energy of formation from the elements of a crystalline oxide and the Gibbs energy of formation from the elements of its cation in aqueous solution (per O2? in the oxide). Another parameter called Δ hydroxide is defined as the difference between the Gibbs energies of formation of an hydroxide and its constituent oxides, H2O oxide being considered as ice. A linear equation for 32 hydroxides, using these two parameters is: Δhydroxide = ?0.210 (ΔO2? cation ? ΔO2? H+). This relation can also be expressed in terms of solution energies. The solution energy of an hydroxide is a linear function of the solution energy of the corresponding oxide. The equation above can be used to predict values for Gibbs energies of formation of hydroxides, oxides or aqueous cations and to test the consistency of existing Gibbs energy values. |
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