Jorge C. G. Calado

Thermodynamics of liquid methane+ethane

The total vapour pressures, the excess Gibbs energy GE (at 90.69 and 103.99 K) and the excess molar volume VE (at 103.99 K) are reported for liquid mixtures of methane and ethane. The results are compared with those obtained by previous investigations and interpreted in the light of some simple theories of liquid mixtures.

THERMODYNAMIC PROPERTIES OF BINARY LIQUID MIXTURES OF ETHANE AND ETHYLENE WITH METHANE AND THE RARE GASES

Two series of binary liquid mixtures containing either ethylene or ethane have been investigated, at one or more temperatures (usually at the triple-point temperature of the component with the higher melting-point). In the ethylene series liquid-vapour equilibrium and liquid density studies were carried out for mixtures with methane, krypton and xenon; the heats of mixing were also measured for the ethylene + krypton mixtures. In the ethane series, which comprised mixtures with methane, argon, krypton and xenon, all three properties were measured except for the ethane + methane and ethane + argon systems where the enthalpies of mixing were already known. The ethylene + ethane system was also investigated at 161.39 K. The results have been used to estimate the thermodynamic excess functions GE , VE and HE . The GE values decrease, within each series, as one moves from the lighter to the heavier rare gas, the values being lower in the ethane series. For the ethane + xenon mixtures both GE and HE are negativ...

Thermodynamics of liquid mixtures of xenon and hydrogen chloride

The total vapour pressure of the system xenon + hydrogen chloride has been measured as a function of composition at 159.07, 182.26 and 195.42 K. The results have been used to estimate the excess Gibbs function GE at these temperatures. The volume of mixing VE has been determined at 195.42 K. The system departs considerably from ideal behaviour, forming a positive azeotrope, and at the lowest temperature is probably not far from an upper critical solution temperature. Estimates have been made of effective Lennard–Jones parameters for the interaction of two hydrogen chloride molecules from the properties of the cubic form of crystalline hydrogen chloride. These have been used to calculate the excess thermodynamic functions of xenon + hydrogen chloride mixtures on the basis of the one-fluid van der Waals theory of Leland, Rowlinson and Sather. To force agreement between the experimental and calculated GE values requires a value of k12 of ∼0.075, where k12 is defined by the equation for the cross intermolecular energy parameter Iµ12, namely Iµ12=(1–k12)(Iµ11Iµ22)½. It is shown on the basis of simple intermolecular force theory that such a value for k12 is reasonable, and that it derives primarily from the permanent dipole–dipole forces between hydrogen chloride molecules.

Surface tension for octafluorocyclobutane, n-butane and their mixtures from 233 K to 254 K, and vapour pressure, excess Gibbs function and excess volume for the mixture at 233 K

Abstract The surface tensions of octafluorocyclobutane (234 to 267 K), n-butane (238 to 273 K) and of their mixtures (232 to 254 K) have been measured by differential capillary rise; there is a slight minimum in the isotherms near x(c-C4F8) ≈ 0.8 but no maximum. The total vapour pressure and density of the liquid mixture were measured at the triple point temperature of c-C4F8, 233 K. The mixture displays marked positive azeotropy. The excess Gibbs function and excess volume are both large and positive but the deviation from ideality is insufficient for liquid—liquid immiscibility whose absence was confirmed by visual observation at temperatures down to the solid—liquid phase boundary. All the foregoing are consistent with theoretical expectations based upon the dominant effect of an interaction energy between the unlike components which is smaller than that predicted by the Berthelot geometric mean rule. No inferences can be drawn as to the role of chain flexibility.

Thermodynamics of liquid (dimethylether + xenon)

Abstract The vapour pressures and densities of { x (CH 3 ) 2 O + (1− x )Xe}(1) have been measured at 182.33 K (the triple-point temperature of dinitrogen oxide). The excess molar enthalpy H m E has been determined calorimetrically at about the same temperature (182.3 K). The excess molar Gibbs energy G m E has been calculated from the vapour pressures. G m E , H m E , and the excess molar entropy S m E are all positive over the whole composition range, their values for x = 0.5 at 182.33 K being G m E = 425.9 J·mol −1 , H m E = 575.2 J·mol −1 , and TS m E = 149.3 J·mol −1 . The excess molar volume V m E is, however, negative with a value, for x = 0.5: V m E = −0.208 cm 3 ·mol −1 . This pair was chosen as a model for a binary liquid mixture in which the molecules of one component are spherical, while those of the other component have a moderately strong dipole moment and a shape which is far from spherical.

The thermodynamic excess functions of krypton+ethene liquid mixtures☆

Abstract Measurements are reported of the total vapour pressure of liquid mixtures of krypton + ethene at the triple-point temperature of krypton (115.77 K) as a function of composition, of the excess molar volumes of the mixtures at the same temperature, and of the excess enthalpy at 117.7 K. These results are compared with those obtained for similar systems, namely methane + ethene and xenon + ethene, and interpreted in the light of some simple theories of liquid mixtures.

Thermodynamics of binary liquid mixtures involving hydrogen bromide, hydrogen chloride and xenon

The total vapour pressure of the systems hydrogen bromide + xenon and hydrogen bromide + hydrogen chloride have been measured as a function of composition at 195.42 K. The results have been used to estimate the excess Gibbs function GE. The volume of mixing VE has been determined for each system at 195.42 K. The HBr + Xe system departs considerably from ideal behaviour, while HBr + HCl is only slightly nonideal. Neither system exhibits an azeotrope at the temperature studied. These results, together with similar data reported previously for the HCl + Xe system (J.C.S. Faraday I, 1975, 71, 1372), are compared with theoretical calculations based on perturbation theory for liquids of nonspherical molecules. Agreement is good for all three systems. The results show that both dipolar and quadrupolar forces for the HCl and HBr molecules have a large effect on the phase diagram, while other types of anisotropic intermolecular forces (overlap, dispersion, induction) appear to have a considerably smaller effect.

Thermodynamics of the xenon+methyl chloride system

Abstract The total vapour pressure of the xenon + methyl chloride system has been measured as a function of composition at 175.44 and 182.32 K. The resulting data have been used to evaluate the excess Gibbs functions GE at the same temperatures. The excess enthalpy and excess molar volume have also been measured at 182.32 K. The system shows large positive deviations from Raoults law but negative volumes on mixing. These results are compared with theoretical predictions of a recent molecular theory and of standard engineering methods. The calculations show the superiority of the molecular theory over more empirical procedures such as those based on the Redlich-Kwong equation of state or the regular-solution model.

Thermodynamics of the liquid system methane + propane

The total vapour pressure of liquid mixtures of methane and propane has been measured as a function of composition at temperatures of 115.77 and 134.83 K. The activity coefficient of methane ƒ1 and the excess Gibbs function of mixing GE have been evaluated from the vapour pressure measurements, and the heat of mixing HE and the excess entropy of mixing SE have been estimated from the temperature dependence of GE and compared with direct calorimetric values. Values of the excess thermodynamic functions have been calculated from a simplified version of the Flory theory of mixtures, with allowance for departures from the geometric mean (Berthelot) combining rule. Calculations show that these deviations are very small, but not negligible.

Liquid-vapour equilibrium of {xBF3 + (1 − x)n-butane} at 195.49 K

The saturation vapour pressure of {x BF3 + (1−x)n-C4H10} has been measured at 195.49 K. The system shows large positive deviations from Raoult’s law and liquid–liquid immiscibility over a wide composition range whose limits have been estimated as 0.39±0.03 0.9785. The excess molar Gibbs energies (G E ) have been calculated as a function of composition from the vapour pressure data. For the hypothetical equimolar mixture G E (x = 0.5) = (703.9 ± 29) J mol −1 . The results were interpreted using the statistical associating fluid theory for potentials of variable range (SAFT-VR), as well as compared with those of related systems, such as (BF3 + n-pentane) and (BF3 + xenon).