Calculation of the transport properties of aqueous species at pressures to 5 KB and temperatures to 1000°C

Abstract

The limiting equivalent conductances at temperatures from 0° to 1000°C and pressures from 1 to 5000 bars of a large number of aqueous ions have been calculated from limiting equivalent conductances of electrolytes reported in the literature. The limiting equivalent conductances of individual ions typically increase by a factor of about 15 with increasing temperatures from 0° to 1000°C and decrease about 30 percent with increasing pressure from 1 to 5 kb. The equivalent conductance of H₂O approximated by the sum of the limiting equivalent conductances of H⁺ and OH⁻ is essentially independent of pressure, but increases from about 350 to a maximum of approximately 1800 S-cm²-equiv⁻¹ in response to an increase in temperature from 0° to 500°C at 1kb. Stokes' law radii and Walden products generated from the computed limiting equivalent conductances of ions exhibit changes over the temperature and pressure range of interest by as much as 100 percent for all of the ions except H⁺ and OH⁻, which vary by an order of magnitude. Apparent solvation numbers calculated as a function of pressure and temperature from the Stokes' law radii using the volume and dielectric constant of H₂O and Born coefficients of the individual ions approach infinity at the critical point of H₂O. Residual friction coefficients as a general rule approach zero as temperatures increases to 1000°C. The excess limiting equivalent conductances of the hydrogen and hydroxyl ions computed from the differences between the limiting equivalent conductances of HCl and KCl, and NaOH and NaCl, respectively, increases with increasing pressure, and maximize at 250°C.