Portal de Periódicos da CAPES

The enthalpy of dilution of aqueous sodium chloride to 673 K using a new heat-flow and liquid-flow microcalorimeter. Excess thermodynamic properties and their pressure coefficients

1984; Elsevier BV; Volume: 16; Issue: 4 Linguagem: Inglês

10.1016/0021-9614(84)90174-5

1096-3626

R. H. Busey, H. F. Holmes, R.E. Mesmer,

thermodynamics and calorimetric analyses

A new heat-flow and liquid-flow calorimeter utilizing a Calvet microcalorimeter is described; it can be used to measure excess enthalpies of liquids at temperatures and pressures up to 700 K and 50 MPa. The sensitivity of the calorimetric apparatus permits observations to be made on sufficiently dilute solutions to allow good extrapolations to infinite dilution required for derivation of excess thermodynamic properties as well as standard-state quantities. The enthalpies of dilution of aqueous solutions of NaCl from 0.1 to 5 mol·kg−1 at temperatures from 323 to 673 K have been measured. Isobaric observations were made at two different pressures at each experimental temperature which permitted derivation of pressure coefficients for the first time. The following excess thermodynamic properties have been calculated from the results from 0.1 to 5 mol·kg−1 at the saturation vapor pressure of water and from 373 K to the temperature indicated: apparent relative molar enthalpy Lφ(623 K), activity coefficient λ(623 K), osmotic coefficient φ(623 K), relative partial molar enthalpy L2(623 K), and excess molar heat capacity Cp, mE(523 K). Pressure coefficients of these excess properties have been calculated from the results. No values of the excess thermodynamic properties for any electrolyte have been previously available above 573 K. In addition, all these excess properties except Cp, mE have been calculated to the supercritical temperature 673 K and 41.5 MPa. Comparisons with values in the literature demonstrate that the calorimeter is capable of precise enthalpy measurements which lead to accurate thermodynamic properties and their pressure coefficients at high temperatures and pressures.