Data and models for calculating the standard thermodynamic properties of aqueous non-electrolyte solutes under hydrothermal conditions

Abstract

The standard chemical potentials μs of aqueous solutes over a wide range of temperatures and pressures are needed to calculate phase and chemical equilibria in hydrothermal systems. The standard derivative thermodynamic properties of solutes such as enthalpies, heat capacities and volumes can be integrated to calculate μs at super-ambient conditions. These derivative properties can be obtained by extrapolation to infinite dilution of calorimetric and volumetric data for aqueous solutions measured as a function of concentration at various temperatures and pressures. A large amount of new experimental results has been reported over the past two decades, which allowed improvement of predictions based on equations of Helgeson, Kirkham and Flowers, among others. Several new thermodynamic models for the standard thermodynamic properties have been proposed during this period. This paper focuses on non-electrolyte solutes and provides an overview of the recent sources of experimental data. We also compare the ability of several thermodynamic models to correlate and predict μs. This paper was presented at «Fluid/minerals Interactions in the Crust», a symposium in honour of Martine Lagache, Paris, October 1999