CACL2(AQ) AT ELEVATED-TEMPERATURES - ENTHALPIES OF DILUTION, ISOPIESTIC MOLALITIES, AND THERMODYNAMIC PROPERTIES

Enthalpies of dilution of CaCI2(aq) have been measured for molalities ranging from 0.008 mol·kg-1 to 7.26 mol · kg-1, at temperatures from about 298 K to 526 K, and for pressures of approximately 7 MPa to 40 M Pa. Isopiestic molalities of CaCI2(aq) were measured over the temperature range of 444 K to 524 K at molalities ranging from 0.55 mol · kg-1 to 4.8 mol · kg-1 with NaCl(aq) serving as the reference electrolyte. The results can be described quite well within the framework of the ion-interaction model. Our results have been combined with other thermodynamic results for CaCl2(aq), including heat capacities and densities, to produce a general model for the thermodynamic properties of CaCl2(aq) which is valid for molalities to 4.6 mol · kg-1 and pressures to 40 MPa over the temperature range 270 K to 526 K. The model is based on the ion-interaction treatment of Pitzer and allows for a small amount of ion association at the highest temperatures by using the β(2) parameter in the second virial coefficient and making the α1 parameter linearly dependent on temperature. For temperatures greater than 523 K, a description of the thermodynamic properties of CaCl2(aq) will require explicit consideration of ion association. © 1994.