Thermodynamics of aqueous sodium chloride to 823 K and 1 kilobar (100 MPa).

It is shown that a very simple semiempirical equation represents quite accurately the thermodynamic properties of aqueous sodium chloride from 373 to 823 K. The equation comprises one Margules term and a Debye-Hückel term. Just the one Margules parameter is freely adjustable because the Debye-Hückel parameter is determined by the properties of water. The equation is valid from the saturation composition down to infinite dilution for solvent density above 0.75 g.cm(-3) but at lower density only above a solute mole fraction of about 0.1 on an ionized basis. Both solute and solvent activity coefficients are fitted from the lowest pressure of solution existence up to 1 kilobar (1 bar = 100 kPA). Derivation of enthalpy and other related functions is discussed.