Lélio Q. Lobo

Thermodynamics of liquid mixtures of xenon and methyl fluoride

Experimental determinations of the vapour—liquid equilibria of Xe + CH3F at 161.39, 182.33, and 195.48 K are presented together with the evaluation of the excess Gibbs energy GE over the entire composition range. The system exhibits a positive azeotrope for solutions richer in the more volatile component (x1 ≈ 0.1). The excess molar enthalpy estimated from the G E values for the equimolar mixture is relatively large and positive (HE = 867 J mol−1). The molar volumes of the liquid mixtures measured at 161.39 K show that for this system VE is small and positive. The experimental results are compared with those obtained by using the Soave and the Peng—Robinson equations of state.

Some thermodynamic properties of liquid hydrogen sulphide and deuterium sulphide

Abstract The orthobaric densities of liquid H 2 S and D 2 S have been measured from about 197 to 265 K. Over the whole of this range, liquid H 2 S has the larger molar volume. The difference of the vapour pressures of the two compounds has been measured from about 208 to 248 K. At 225.05 K the two liquids have the same vapour pressure. At lower temperatures than this, H 2 S has the higher vapour pressure. The available vapour pressures for H 2 S have been fitted to a Wagner equation. By combining vapour pressures for H 2 S derived from this equation with the differential measurements, values for the vapour pressure of D 2 S have been obtained. These values have also been fitted to a Wagner equation. The material presented in this paper has been used to estimate the enthalpy of vaporization of H 2 S and of D 2 S each from its triple-point temperature to 270 K. Throughout this temperature range, the enthalpy of vaporization of D 2 S exceeds that of H 2 S, the difference decreasing with rising temperature.

Some thermodynamic properties of liquid ammonia and trideuteroammonia

Abstract The orthobaric density of liquid NH 3 has been measured from about 200 to 287 K, and for liquid ND 3 from about 205 to 273 K. The molar volume of liquid NH 3 exceeds that of ND 3 by between 0.8 and 0.9 per cent. The difference of the vapour pressures of the two compounds has been measured from about 200 to 266 K, and the vapour pressure of NH 3 from the triple-point temperature to 234 K. Liquid NH 3 has the higher vapour pressure, the difference being relatively large for a pair of isotopic compounds. At 200 K, the ratio of the vapour pressure of NH 3 to that of ND 3 is about 1.2. The available vapour pressures for NH 3 have been fitted to a Wagner equation. By combining vapour pressures derived from this equation with the differential measurements, values for the vapour pressure of ND 3 have been obtained. These values have likewise been fitted to a Wagner equation. The material presented in this paper has been used to estimate the molar enthalpies of vaporization of NH 3 (l) and of ND 3 (l) from the triple-point temperatures to 290 K. The molar enthalpy of vaporization of ND 3 exceeds that of NH 3 throughout this range. The difference amounts to about 3.5 per cent at the triple-point temperatures, and decreases with rising temperature.

Some thermodynamic properties of hydrogen chloride and deuterium chloride

Abstract The molar volume V m l of HCl(l) has been measured from 162 to 236 K, and of DCl(l) from 160 to 218 K. The difference in V m l of the two compounds in this range does not exceed 0.1 per cent. At lower temperatures, V m l (HCl) > V m l (DCl), but from 192 K upwards V m l (HCl) V m l (DCl). Direct measurements of the vapour pressure of HCl have been made from 159 to 220 K, and of DCl from 158 to 188 K. In addition, the difference in the vapour pressure of the two isotopic forms has been measured from 159 to 226 K. At lower temperatures, the vapour pressure of HCl exceeds that of DCl but above 223.35 K that position is reversed. The vapour pressure of each substance has been fitted to a Wagner equation. These equations have been used in conjunction with the Clapeyron equation to calculate the molar enthalpies of vaporization Δ l g H m . If r is the ratio of the vapour pressure of HCl to that of DCl, the values of r conform very closely to the equation T ln r = − A + C T , where A and C are constants. This has been used in an alternative way of estimating the difference in Δ l g H m for the two compounds. At 160 K, Δ l g H m of DCl exceeds that of HCl by 260 J · mol −1 . This difference decreases with rising temperature, being 138 J · mol −1 at 230 K. If the estimate of Δ l g H m for DCl is combined with the results of Chihara and Inaba, the calorimetric (third-law) entropy of DCl in the ideal-gaseous state at 101 325 Pa and 188.50 K, its normal boiling temperature, is 179.25 J · K −1 · mol −1 , in agreement with the statistical value.

Thermodynamics of liquid mixtures of nitrous oxide and ethene

Experimental determinations of the vapour pressures, molar volumes and heats of mixing are reported for liquid mixtures of ethene and nitrous oxide at temperatures close to the triple-point temperature of nitrous oxide (182.32 K). From these measurements the excess volume. Gibbs free energy and enthalpy are derived. The excess Gibbs energy and the excess enthalpy are found to be positive, almost symmetric functions of composition, with values at the equimolar composition of 168.9 J mol–1 and 270.9 J mol–1, respectively. The excess volume, on the other hand, is found to be negative and displays a highly skewed composition dependence, the minimum occurring at xN2O≈ 0.96.These results were examined theoretically by the use of a perturbation theory based on spherical reference molecules. The importance of using a full non-axial treatment of the quadrupolar interactions between constituent molecules of the mixture is demonstrated. The effect of contributions to the free energy from the quadrupole–dispersion, anisotropic–dispersion and shape forces is shown to be of considerable importance in predicting the excess enthalpy. None of the intermolecular potential models studied was able to reproduce the shape of the excess-volume curve.

Thermodynamics of liquid mixtures of xenon and carbon tetrafluoride

The total vapour pressure, excess enthalpy and excess volume of the system carbon tetrafluoride + xenon have been measured as a function of composition; the vapour pressure and excess volume measurements are at 159.01 K (the triple-point of HCl) and those for the excess enthalpy are at 163.01 K. The vapour pressure results have been used to estimate the excess Gibbs energy. The mixture exhibits a positive azeotrope at a xenon mole fraction of ca. 0.19. The experimental results are compared with values calculated from perturbation theory for non-spherical molecules, using an intermolecular potential model that includes octopole–octopole and anisotropic dispersion and overlap terms. Agreement is good for both the pure fluid and mixture properties.

VLE for cryogenic methyl fluoride + nitrous oxide + xenon at 182.33 K

An apparatus for accurate VLE measurements on ternary cryogenic systems is briefly described. It is a modified version of that introduced and developed by Staveley and co-workers for binary mixtures. The apparatus was tested against published results for CH 3F + Xe and N20 + Xe, at 182.33 K, the agreement being much satisfactory for both systems. The mixture CH3F + N20 + Xe at the same temperature was selected for the first measurements on a ternary system carried out using the modified experimental arrangement, the operation of which is also summarized. VLE results for 61 ternary points are presented together with the evaluation of the excess molar Gibbs free energy G E for the liquid mixture at that temperature. No ternary azeotrope has been found. G E for the three component liquid mixture is not an additive function of the G~ for its constituent binary mixtures. For the equimolar (ternary) mixture G~/3 = (500 -4- 6) J mol -~ , at 182.33 K.

Enthalpy of mixing of liquid hydrogen chloride and liquid xenon. Comparison of experiment and theory

Calorimetric measurements are reported for the enthalpy of mixing HE of liquid hydrogen chloride and liquid xenon at 182.32 K. These results are compared with values calculated from perturbation theory, using two slightly different sets of intermolecular potential models for the Xe + HCl system. Although these models give good results for the excess Gibbs energy GE and excess volume VE, they are found to give values that are too high for HE.

Solubility of methyl fluoride in some alcohols

The solubilities of methyl fluoride in some polar solvents (methanol, ethanol, propanol and n-butanol) have been measured at temperatures ranging from about 280 to 300 K, and at atmospheric pressure. The solubility is the lowest in methanol, increasing with the C-content of the alcohols. H-bonding factors, based on the ideal gas solubilities and the solubilities in the alcohols, appear to be linearly dependent on the H-bonding factor in methanol. The molar Gibbs energy, enthalpy and entropy of solution were calculated from the experimental results (at 1 atm partial pressure of the gas and 298 K).

Error analysis in Barker's method: extension to ternary systems

Abstract An extension of Barkers method to ternary systems is briefly outlined. Expressions for the standard deviations of the excess molar Gibbs free energy and the equilibrium pressure as functions of composition are obtained. These expressions are applied to accurate experimental data for the cryogenic (liquid) mixture CH3F+N2O+Xe recently measured in our laboratory.