Thermodynamic properties of NaCl solutions at temperatures lower than 0 degrees C

The limiting values of NaCl(aq) heat capacity, c(p,2)(0), at temperatures f rom 0 to -25 degrees C and volume, V-2(0), from 0 to -15 degrees C, were ob tained by the mathematical processing of experimental determinations of hea t capacity and density of sodium chloride solutions at temperatures lower t han 0 degrees C. Proceeding from these results, the parameters of the Helge son-Kirkham-Flowers (HKF) equation of state were refined for the species Na +. The Gibbs free energies of Na+ and Cl- calculated by the HKF equation to gether with the modified approximations of Fitter's parameters for calculat ion of activity coefficients allowed numerical reproduction of the experime ntal NaCl-H2O phase diagram. This proves the validity of the HKF model for the extrapolation of the limiting thermodynamic properties of aqueous speci es into low temperatures. The thermodynamic parameters of Na+ and Cl- deriv ed in this work; enable precise thermodynamic calculations in the system Na Cl-H2O at temperatures from 100 to -30 degrees C and a wide range of electr olyte concentration.