Equations that described the thermodynamic properties of the NaCI + H20 system were obtained from a fit to experimental results for this system. The experimental results included in the fit spanned the range of temperature of approximately 250 to 600 K and, where available, the range of pressure from the vapor pressure of the solution to 100 MPa. New equations and/or values for the following properties are given in the present work: 1) A~~ and An:.. for formation from the elements. for NaCI(cr) for 298.15 K and 0.1 MPa, 2) A~:' and An:. from the elements, as well as S:' and C;'m, all for 298.15 K, 0.1 MPa, for NaCI'2H20(cr), 3) the change in chemical potential for both NaCI and HzO in NaCI(aq) as a function of temperature, pressure, and molality, valld from 250 to 600 K and, where available, from the vapor pressure of the solution to 100 MPa. Comparison of the accuracies of experimental methods, where possible, has also been performed.

Experimental values of the dielectric constant of water suggest that, for temperatures greater than 400 K, the integral in the Kirkwood dielectric-constant equation, which involves the intermolecular potential function, is a simpler function of temperature and pressure than of temperature and density. An equation has been fitted to values of this integral calculated from experimental values of the dielectric constant for temperatures from 238.15 K to 823.15 K and to pressures of approximately 500 MPa for temperatures greater than 273 K. The equation for E thus has explicit variables T, p, P and gives a good representation of the available experimental results. The quality of representation of the experimental results has been compared to that of previous correlations of the dielectric constant. The new equation is applicable through wider regions of imlepenuent variables than the previous equations and is capable of sufficient accuracy to provide values of Debye-Hiickel limiting law slopes which are as accurate as the experimental results allow. Values of Dehye-Hiickel limiting-law slopes are tabulated.

Comparison of the National Institute of Standards and Technology's Standard Reference Material 720 certificate values for heat capacity with those obtained from recent experimental determinations indicated the possibility of a systematic error in the certificate values. Selected experimental determinations of enthalpy increments and heat capacities were fitted in order to obtain a representation of the thermodynamic properties of a-Ab03, a sample of which is the standard reference material (SRM720) for calibration of some types of calorimeters. The fitted equation and calculated values of the heat capacity, the relative enthalpy, and the entropy are given. The new values are more accurate and result from a better representation of the experimental values than did the 1982 SRM720 certificate values. Additionally, the general problem of the effect of changes in practical temperature scales on ther-mOdynamic properties is briefly discussed, using the results fur a:-Ah03. A recent report from the IUP AC Commission on Thermodynamics gave a method for the conversion of thermodynamic properties for changes in practical temperature scale. The IUPAC method is shown to be not generally correct. A better methorl for estimation of these changes is given.

No abstract

Equations that described the thermodynamic properties of the NaBr + H 2 0 system were obtained from a fit to experimental results for this system. The experimental results included in the fit spanned the range of temperature of approximately 260 to 623 K and the range of pressure from the vapor pressure of the solution to 150 MPa. New equations and/or values for the fonowing properties are given in the present work: 1) the change in chemical poten.tial with respect to temperature and pressure for NaBr(cr), valid from 200 to 900 K, 2) ~fG~and .6.fH~for formation from the elements for NaBr(cr) for 298.15 K and 0.1 MPa, 3) A.fG~ and Ad/rit from the elements, as well as S~ and C;, m, all for 298.15 K, 0.1 MPa for NaBr-2H 2 0(cr), 4) the change in chemical potential for both NaBr and H20 in NaBr(aq) as a function of temperature, pressure, and molality, valid from 260 to 600 K and from the vapor pressure of the solution to 150 MPa.

The thermodynamic properties of the KCl+H2O system were examined in order to provide: (1) an improved equation for the osmotic coefficient as a function of molality and temperature for purposes of isopiestic measurements, (2) a determination of the thermodynamic properties of the standard-state solution process, and (3) a test of the accuracy of the enthalpy of solution values for KCl(cr), a calorimetric standard. New equations that describe the thermodynamic properties of the KCl+H2O system were obtained from previously published measurements for this system. The measured values included in the fitted equations spanned the range of temperature from approximately 260 to 420 K for KCl(aq) and 1.5 K to 1033.7 K for KCl(cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of KCl(cr) from 0 K to the melting point, 1045 K, (2) the change in chemical potential for both KCl and H2O in KCl(aq) as a function of temperature, and molality, valid from 260 to 420 K, and (3) standard-state properties for the aqueous solution process. The effect of heat treatment on the determination of enthalpy of solution values was also examined. This examination indicated that the NIST recommendation of heating Standard Reference Material 1655, potassium chloride, at 800 K for a minimum of 4 h prior to its use in calorimeter calibration, should probably not be followed. The heat treatment recommended by the NIST certificate appears, at this point, to have a higher probability of corrupting the sample than improving the accuracy of the measurement.

No abstract

The available experimental thermodynamic data for NaCI(cr) have been fitted in order to generate thermodynamic values as a function of temperature and for a nominal pressure of 0.1 MPa. Thermal measurements (heat-capacity values and enthalpy-increment values) have been fitted with a new method. The fitted function and calculated thermodynamic values are given. Estimates of the inaccuracies of the calculated thermodynamic values are also given.