Hydrothermal organic reactions occur in many geochemical processes. While ambient reactions are often kinetically controlled, evidence from natural systems and experiments suggests metastable equilibria, which in turn supports a major role for thermodynamic modeling in studies of hydrothermal reaction pathways. Here we report calculations of the hydration Gibbs energies of organic compounds at high temperature ?hG(T) using ab initio computations. ?hG�, the hydration Gibbs energy of a solute at the reference conditions was determined ab initio with Cramer and Truhlar's SMD solvation model based on solute charge density and polarizable continuum model. ?hG(T) was determined empirically from ?hG� via KD(T), the vapor-liquid distribution constant of the solute at high temperature, and the Krichevskii parameter, which characterizes thermodynamic functions of infinitely dilute solutions near the solvent's critical point. Values of ?hG(T) for small organic molecules estimated from KD(T) at 300�C can be within 1 kcal/mol of thermodynamic predictions based on experimentally determined KD.

Hydration Gibbs energies in water at high temperature:  A combined ab initio and empirical approach

243rd National Meeting (2012)

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