Search

The method developed in a previous paper [R. Mazo, J. Chem. Phys. 129, 154101 (2008)] for extracting information on the size of relative fluctuations in multicomponent systems is tested on ten binary systems and one ternary system. For the binary systems, it is found that the approximation works well for mole fractions in the range of 0.15-0.85 in most cases. For the ternary case, the method inherently yields less information and is valid only over a more restricted range for the case studied (chloroform-methanol-acetone). It is found that the predicted ratio of number fluctuations is approximately equal to the ratio of molar volumes of the components.

Vapor–liquid equilibria of binary mixtures of n -heptane with 15 amines, primary n -alkyl (C3–C8), secondary (diethyl to dibutyl), branched ( iso -propyl and sec -butyl) and cyclic amines (piperidine, hexamethyleneimine, heptamethyleneimine and cyclopentylamine) have been determined by head-space gas chromatographic analysis of the vapor phase directly withdrawn from an equilibration apparatus. Excess molar Gibbs energies and activity coefficients for the systems investigated have been obtained by a least-square treatment of the equilibrium results. All mixtures exhibit positive deviations from ideality, decreasing with the amine size. The Gibbs energy of solvation for amines in heptane has been evaluated and its dependence on polar groups, chain lengthening, branching and cyclization has been discussed. [ABSTRACT FROM AUTHOR]

The standard thermodynamic parameters (Δ G°, Δ H°, and TΔ S°) of the reaction of molecular complex formation of 18-crown-6 ether (18C6) with d, l-alanine (Ala), [Ala18C6], have been obtained from calorimetric titration experiments carried out using the microcalorimetric system TAM III (TA Instruments, USA) at T = 298.15 K in water-ethanol (HO-EtOH) solvents at X = 0 ÷ 0.6 mol fractions. Results show that the increase of the EtOH concentration in solvent brings about an increase of the [Ala18C6] complex stability and of the exothermicity of the reaction of complex formation. The solvation contributions of 18C6, Ala, [Ala18C6] to Δ G° and Δ H° at various X values are also analyzed. [ABSTRACT FROM AUTHOR]

The influence of H2O–EtOH and H2O–Acetone mixed solvents at various compositions on the thermodynamics of complex formation reaction between crown ether 18-crown-6 (18C6) and glycine (Gly) was studied. The standard thermodynamic parameters of the complex [Gly18C6] (log K°, Δr H°, Δr S°) were calculated from thermochemical data at 298.15 K obtained by titration calorimetry. The complex stability and its formation enthalpy increase with increasing the non aqueous component concentration in both mixed solvents. The thermodynamic data were discussed on the basis of the solvation thermodynamic approach and the solvation contributions of the reagents and of the complex to the complex stability were analyzed. [ABSTRACT FROM AUTHOR]

Literature data on molar excess enthalpies and molar excess Gibbs energies, liquid-liquid equilibria, activity coefficients at infinite dilution and partial molar enthalpies at infinite dilution of binary mixtures of n-perfluoroalkanes (C5−C8)+ n-alkanes (C5−C8) and of n-perfluorohexane-linear monoethers of general formula, CH3(CH2)m-O-(CH2)n-CH3 ( m,n=1–4), are treated in the framework of DISQUAC, an extended quasichemical group contribution theory. The systems are characterized by two or three types of contact surfaces: aliphatic (CH3, CH2, CH and C groups), fluorine (F group) and oxygen (O group). Using a limited number of adjusted contact interchange energies parameters, structure dependent, the model provides a fairly consistent description of the thermodynamic properties as a function of concentration. The model may serve to predict missing data. [ABSTRACT FROM AUTHOR]

A newly designed calorimetric technique and calculation procedure has been used to obtain partial molar enthalpies and excess enthalpies HE at 298.15 K for binary mixtures of heptane + primary n-alkyl (C3–C10) and branched (iso-propyl, sec-, iso-, and tert-butyl) amines in the whole composition range. All mixtures examined showed positive HE, which decrease with increasing amine size. From partial molar enthalpies at infinite dilution and from the known enthalpies of vaporization, the enthalpies of solvation ΔsolvH° have been evaluated either for amines in heptane and heptane in amines. An additive scheme of surface interactions combined with the scaled particle theory (SPT) is presented to estimate and analyse different group (CH3, CH2, CH, C, NH2, O, OH, CO, CN, COO, CHO) contributions to ΔsolvH° as well as to its cavitational and interactional terms. [Copyright &y& Elsevier]

Abstract: The influence of water–ethanol mixture composition on the complex formation between 18-crown-6 ether and l-phenylalanine was studied by titration calorimetry at Т =298.15K. The standard thermodynamic parameters (Δr G о, Δr H о, ТΔr S о) of formation of [Phe18C6] molecular complex were calculated from data obtained by means of the microcalorimetric system TAM III (TA Instruments, USA) at X(EtOH)=0.0/0.6mol fraction. The stability of [Phe18C6] and the mechanism of complexation in water were investigated using the 1Н and 13С NMR spectroscopy. The increase of EtOH concentration results in an increase of the complex stability and of the exothermicity of complexation. [Copyright &y& Elsevier]

Abstract: The excess enthalpies, H E, at 298.15K for binary mixtures of 1,1,2,2-tetrachloroethane (TCE)+an hydrocarbon (n-heptane, cyclohexane, benzene, toluene, ethyl-, n-propyl-, iso-propyl-, n-butyl-, sec-butyl-, and tert-butylbenzene) have been measured by flow microcalorimetry. All mixtures containing an aromatic hydrocarbon as second constituent exhibit negative H E, while mixtures with n-heptane or cyclohexane are endothermic. The H E data have been analysed in terms of the DISQUAC model. Using a limited number of adjusted interchange energy parameters, C, taken as structure dependent, the model provides a fairly consistent description of H E as a function of concentration. The enthalpies of solvation, ΔH°, of hydrocarbons in TCE, as obtained from heats of solution at infinite dilution and known vaporization enthalpies, have been described using an additive scheme of surface interactions. The effects of aromatic ring, chain lengthening, branching, and cyclization on both H E and ΔH° have been discussed. [Copyright &y& Elsevier]