The difference in densities between water and aqueous solutions of argon, ethylene, and xenon were measured at temperatures from 298 to 720 K and pressures between 20 and 34 MPa by using a vibrating tube densimeter developed in our laboratory. The apparent molar volumes of these gases in water were calculated. For all three gases the volumes go through a maximum as temperature is increased at constant pressure. The compressibility of pure water goes through a maximum at very nearly the same temperature. The magnitude of the maximum increases and shifts to a lower temperature as the pressure decreases. The maximum in apparent molar volume of all three gases is approximately 1000 cm3 mol"* l1 at 34 MPa and about 2500 cm3 mol"1 at 26.7 MPa. These very high apparent molar volumes occur near the critical point of the solvent.
Henry's law constants, kH, at saturation pressure derived from solubility data. bkH calculated from solubility and corrected to 17.2 MPa by using In kH(P2,T) = In k^lP^T) + ffy (V2"/RT) dP, where Vf°i s the partial molar volume at infinite dilution of the solute. c kH calculated from heat capacity data in ref 3. d 2skH = kH at 17.2 MPa derived from solubility data -kH at 17.2 MPa derived from heat capacity data. "Solubility data from ref 19. /Solubility data from ref 27.in Figure 2. There is qualitative agreement between the results. The maximum is in the correct place, but the calculated values are too low at temperatures below the maximum and too high above the maximum. Presumably, better agreement would be found for measurements closer to infinite dilution and closer to the critical point.The theoretical and experimental findings that V2°i s proportional to kt shows that any theory or correlation must include this factor in order to work well near the critical point. The corresponding-states treatment of Brelvi and O'Connel33 includes this factor. The scaled particle theory of gas solubility34 and the perturbation theory of Neff and McQuarrie32 give reasonable results only if the experimental value of the solvent density and its temperature derivative are used in the calculation since this builds in the experimental value of T for water. Marshall and co-workers have correlated chemical equilibria as simple functions of the density of the solvent and the temperature.36 38 This procedure gives terms proportional to kt for , and these equations can fit data near the critical point.
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