VOLUMES AND HEAT-CAPACITIES OF AQUEOUS-SOLUTIONS OF HYDROCHLORIC-ACIDAT TEMPERATURES FROM 298.15 K TO 623 K AND PRESSURES TO 28 MPA

Densities of aqueous solutions of HCL at molalities from O.1 mol . kg( -1), to 6.0 mol . kg(-1), temperatures from 298.15K to 623 K, and pres sures of 10 MPa and 28 MPa have been measured with a vibrating-tube fl ow densimeter. Heat capacities of the above solutions at temperatures from 302 K to 623 K and a pressure of 28 MPa were measured using a flo w heat-capacity calorimeter. Standard-slate values for the volumes and heat capacities have been obtained from the apparent molar properties by extrapolation to infinite dilution using the Fitter ion-interactio n model. Our experimental results were combined with available literat ure results on volumes and heat capacities to derive appropriate equat ions for the temperature and pressure dependencies of the Fitter model . The volumetric and heal capacity results for HCL(aq) are in good agr eement with published values al low temperatures. Al higher temperatur es, the qualitative behavior of volumes and heat capacities for HCL (a q) shows clearly the transition from a fully dissociated strong electr olyte to an almost completely ion-paired weak electrolyte. Standard-st ate values calculated from this work are consistent with the literatur e values for the volume and heal capacity change on the ionization of water. (C) 1997 Academic Press Limited.