Thermodynamics of molecular interactions in ethyl iodide+toluene mixtures

The excess Gibb's free energy of mixing, G^E, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The H^E and G^E values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and G^E>H^E. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A₂B molecular species describes well (within±10 J-mol^–1 in the worst case) the general dependence of H^E on X_A (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A AB and 2A+BA₂B reactions along with the enthalpies of formation of AB and A₂B molecular species have been calculated.     

Correlation of the Prigogine-Flory theory with isothermal compressibility and excess enthalpy data for cyclohexane + alkane mixtures

The Prigogine-Flory theory is applied to isothermal compressibilities, at 25, 35, 45 and 60°C and to heats of mixing at 25°C for cyclohexane + n-alkane systems. To this purpose, the van der Waals and the Lennard-Jones potentials have been adopted. The energy parameter ₁₂ has been calculated from the experimental data, and its dependence on the n-alkane number of carbons has been studied. Taking the ₁₂ value obtained for the equimolecular mixture, the excess functi¹/ns (V^E/P)_T, H^E and V^E have been calculated and the results compared with experimental values.     

Thermodynamic excess properties of alkanol + amine mixtures and application of the ERAS model

New experimental data of the molar excess volume V ^E of the mixtures ethanol/n-butylamine, heptanol/n-butylamine, n-propanol/dibutylamine have been obtained using the technique of the vibrating tube densitometer. Together with the data for the molar excess enthalpy H ^E from the literature, the V ^E data have been used for testing the applicability of the socalled ERAS model which accounts for hydrogen bonding effects as well as for free volume effects in associating mixtures. The results obtained by adjusting the model parameters reveal a strong cross association between the unlike molecules in the mixture resulting from strong negative values for the hydrogen bonding energy and the hydrogen bonding volume.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990.     

Thermodynamics of the ternary mixture propan-1-ol + tetrahydrofuran + n-heptane at 298.15 K. Experimental results and ERAS model calculations of G, H and V

Excess molar enthalpies H^E and excess molar volumes V^E have been measured at 298.15 K and 0.1 MPa for the ternary mixture tetrahydrofuran (THF) + propan-1-ol (PrOH) + n-heptane including the three binary mixtures using flow calorimetry and a vibrating tube densitometer, respectively.

Molar excess Gibbs energies G^E have been measured at 298.15 K using a static VLE apparatus equipped with a chromatographic sampling technique for the vapor phase as well as for the liquid phase. Experimental results have been compared with predictions of the ERAS model.     

Estimation of the Nitta-Chao Parameters for the ether-group. Ether + n-alkane mixtures

In this work we have estimated the structural and interactional parameters of the ether- group for the group-contribution model of Nitta-Chao using a extensive experimental database of thermodynamic properties of ethers (monoethers, polyethers and acetals) and ether + n-alkane and ether + ether mixtures. The results obtained by Nitta-Chao model with this parameters get closer to the experimental values than those obtained with parameters of Eckart et al. (1986). The thermodynamic properties obtained by the Nitta-Chao model with old and new parameters were compared to predictions by other models such as Flory (1965) theory, DISQUAC (Kehiaian, 1977) model and UNIFAC model (versions of Dang and Tassios, 1986, and Larsen et al., 1987).     

Thermodynamics of liquid mixtures of argon+ carbon monoxide

The heat of mixing of liquid argon (component 1) and liquid carbon monoxide has been measured by direct calorimetry for several mixtures of composition ranging from x₁ ? 0.2 to x₁ ? 0.8 at 85.79 K. At this temperature H^E is positive and an almost parabolic function of mole fraction, with a maximum value of H^E = 95.9 J mol^?1 at x₁ = 0.569.The experimental results are compared with those derived from the Gibbons-Rigby equation of state, and from conformal solution theory.     

Speed of sound and isentropic compressibilities of nonelectrolyte liquid mixtures. I. Binary mixtures containingp-dioxane

The speed of sound was measured for mixtures of p-dioxane with cyclohexane, n-hexane, benzene, toluene, carbon tetrachloride, chloroform, 1,1,2,2-tetrachloroethane, pentachloroethane and ethyl acetate over the whole mole fraction range at 30°C. These data were combined with densities and molar volumes to obtain isentropic compressibilities and Rao's molar sound functions. Excess isentropic compressibilities and excess speeds of sound have also been calculated. The behavior of the present mixtures is discussed in terms of possible molecular interactions and the Prigogine-Flory-Patterson theory of liquid mixtures.     

Analysis of the intramolecular proximity effect on dichloroalkane + alkane mixtures using Nitta-Chao model

Literature data for vapor liquid equilibria, activity coefficients at infinite dilution, enthalpies of mixing, volumes of mixing of ,ω-dichloroalkane (ClCH₂---(CH₂)_m−2---CH₂Cl, from M=1 to 6) + − alkane mixtures together with vaporization enthalpies and molar volumes of pure dichloroalkanes were examined on the basis of the Nitta-Chao model. In this paper structure-dependent interaction energetic coefficients for this model were presented for a first time. According to the proximity effect when the two chloro groups of the chloroalkane are more separated they become independent and the reported values of the energetic parameters approach to these of the 1-chloroalkane. Similar trends were reported previously for several authors in the framework of the DISQUAC model. A comparison with the predictions of DISQUAC and UNIFAC (version of Larsen et al.) is presented.     

Anomalies in the twist elastic behaviour of mixtures of calamitic and bent-core liquid crystals

ABSTRACT

The splay, twist and bend elastic constants (K₁₁, K₂₂ and K₃₃) have been measured as a function of temperature in bent-core/calamitic mixtures based on three different calamitic materials (5CB, 8CB and ZLI1132) and two bent-core dopants. The behaviour of the splay and bend constants are as expected; a reduction in K₃₃ of ~20%, in line with predictions from mixing rules and other observations. Interestingly, no change is seen in the splay constant, K₁₁ of the calamitic hosts. Surprisingly though, the twist elastic constant exhibits a reduction of 30 – 40% in all mixtures across the nematic range, an effect not previously reported and much larger than mixing rules can explain. The elastic behaviour is universal in our mixtures. We explain part of the reduction in the twist deformation by considering the influence of the chiral conformer fluctuations of the bent-core molecules on the twist elastic constants of the mixtures. However, the dramatic reduction can only be fully explained by also including contributions from chiral conformer fluctuations of the calamitic host, a form of chiral amplification.     

An equation-of-state-based viscosity model for non-ideal liquid mixtures

A viscosity model based on the Eyring’s theory and a cubic equation of state (Peng–Robinson–Stryjek–Vera) has been applied to the correlation and prediction of experimental liquid viscosities of binary mixtures containing polar fluids within a wide range of temperature, pressure and composition (encompassing low-pressure and compressed liquid conditions). Highly non-idealities of the binary mixtures considered in this study were conveniently handled via the application of the Wong–Sandler approach for the mixing rules used in the cubic equation of state. The results obtained were highly satisfactory for various non-ideal binary mixtures over the whole composition range at a low pressure. The predictive capabilities of the present approach were also verified in the representation of liquid viscosities at elevated pressures preserving the same model parameters previously obtained at low pressure.     

Treatment of excess thermodynamic quantities for liquid mixtures

Thermodynamic data on mixtures of liquids are usually expressed as excess quantitiesY ^EX and analyzed with the Redlich-Kister equation. This approach can in some cases be misleading and hide strong interactions at low concentrations. In agreement with the original statement of Redlich and Kister, it is therefore better to plot such data asY ^EX/X ₂(1-X ₂). This quantity, which is directly related to the apparent molar quantities of both components, is often a more useful quantity and has just as much a thermodynamic significance asY ^EX.     

Caloric properties of mixtures of refrigerants R22 / R114

The nonazeotropic refrigerant mixture chlorodifluoromethane (R22) and 1,2-dichlorotetrafluoroethane (R114) has been frequently suggested as a working fluid in cooling systems and heat pump applications. However, especially for mixtures exact and reliable measurements of the caloric properties are often missing, so that calculations with equations of state yield results of great uncertainty. In spite of the CFC-ozone problem of this mixture it can be considered as an exemplary mixture to set up accurate equations of state.

Therefore measurements with an isenthalpic throttle calorimeter were carried out for three different compositions of the mixture. The measured isenthalps could be reproduced within the experimental accuracy by polynomials. Together with the specific heat capacity of the pure components the measurements lead to several caloric properties in the liquid-, vapour- and critical region. The caloric properties can also be calculated by equations of state (EOS). It turned out that the results obtained from Bender's EOS with interaction parameters fitted to the experiments lead to a good agreement with the experimental data.     

A one-parameter group-contribution model for liquid mixtures

A new group-contribution method for the estimation of liquid-phase activity coefficients is presented which uses only one energy parameter per group/group interaction. The development is accomplished theoretically rather than by reinterpreting the terms of a molecular model. Comparative results of predictions using the new model and UNIFAC are given.     

Variation of excess volumes with temperature for binary mixtures ofp-xylene withn-hexane andn-hexadecane

The variation of the molar volume with temperature from 25 to 50 °C of binary mixtures of p-xylene + n-hexane and p-xylene + n-hexadecane has been measured by a dilatometric method over the complete mole fraction range. From the experimental results we have calculated v^E/T)_p. Literature values of v^E at 25°C together with the integration of v^E/T)_p yield v^E as a function of temperature. The excess volumes of p-xylene + n-hexane at 40 °C and p-xylene + n-hexadecane at 40 and 45 °C have also been measured by a dilatometric method, and the results were compared to those obtained from the integration of . The results from both methods are in excellent agreement within experimental error.The experimental values of are negative for the system p-xylene + n-hexane and positive for p-xylene + n-hexadecane. We have interpreted our experimental results in terms of the order present in p-xylene and n-alkanes.     

Flow microcalorimetry and thermokinetics of liquid mixtures

The identification of the calorimetric curves corresponding to liquid mixtures for different injection flows, given by a flow microcalorimeter, permits to classify in a kinetic way the studied mixtures. For this purpose, it is determined the establishment time constant of the mixture (τ_mix) that allows us to estimate the length occupied by the dissipation (through the parameter λ_mix) and thus to justify the sensitivity variation obtained in different chemical calibrations.     

Enthalpies of mixing of binary and ternary mixtures containing diisopropylether,benzene and cyclohexane at 303.15 K

Enthalpies of mixing H have been measured for liquid binary mixtures of diisopropylether (DIPE)+benzene or cyclohexane and for liquid ternary mixtures diisopropylether+benzene+cyclohexane at 303.15 K and constant pressure using a C80 calorimeter. A Redlich-Kister type equation was used to correlate experimental results.     

Thermodynamics of aqueous mixtures of nonelectrolytes. I. Excess volumes of water-n-alcohol mixtures at several temperatures

Excess volumes of binary mixtures of water with methanol, ethanol and 1-propanol were obtained from density measurements at 5 degree intervals from 15 to 35°C over the entire composition range. Excess thermal expansion coefficients, partial molar excess volumes, and expansibilities at 25°C were derived from the results. The significance of these values is discussed in relation to hypothesized structural changes in the mixtures.     

Liquids and liquid mixtures: Deduction of the BGY equation considering the angular distribution function

The Born→Green→Yvon equation for molecular fluid has been deduced considering the orientational distribution functions. The isotropic and anisotropic parts of the distribution function have been separated. The expressions deduced can be used in the case of mixtures and for the non-central type of intermolecular potential energy.     

Excess volume of mixing and equation of state theories

Equation-of state theories of Flory and of Sanchez and Lacombe describe both enthalpy and volume of mixing of binary systems using single component properties and only one binary parameter X₁₂. We have evaluated this parameter from literature enthalpy data for numerous mixtures of two aromatic hydrocarbons, of alkanes with aromatic compounds, and of alkanes with carbonyl compounds. We have used this X₁₂ for calculation of excess volumes and compared the results with our previously measured experimental data. The agreement was fair for mixtures of two nonpolar components. Nevertheless, mixtures containing either cyclohexane or benzene displayed anomalies that could be traced to special packing of molecules in these compounds when pure. For mixtures of carbonyl compounds with alkanes, the theories predicted the qualitative trends correctly, but the quantitative agreement was rather poor. These results tend to support a model in which the enthalpy(cohesive energy) is inversely proportional to volume (as in the theories considered) only for dispersive interaction. When polar-polar interactions are involved, the dependence of excess volume on the excess enthalpy is much weaker.