The Journal of Chemical Thermodynamics (v.38, #12)

Author Index 38 (XI-XV).

With the specific aim of calculating the acidity equilibrium constant (K a) of carboxylic acids in aqueous solution we investigated the solute–solvent interactions of these acids and their corresponding anions. The pK a (−lg  K a) values have been calculated using density functional theory (DFT). The polarized continuum model (PCM) is used to describe the solvent. Using these methods, we successfully predicted the pK as of 66 carboxylic acids in aqueous with the average error of 0.5 in pK a units. Two different thermodynamic cycles have been studied. The theoretical values are in better agreement with the experimental results for those acids with moderate strength of acidity with the pK a value higher than 3.
Keywords: Density functional theory; Carboxylic acids; pK a; PCM;

(Liquid + liquid) equilibria of (water + propionic acid + alcohol) ternary systems by Ş. İsmail Kırbaşlar; Selin Şahin; Mehmet Bilgin (1503-1509).
(Liquid + liquid) equilibrium (LLE) data of the solubility (binodal) curves and tie-line end composition were examined for mixtures of {water (1) + propionic acid (2) + octanol or nonanol or decanol or dodecanol (3)} at T  = 298.15 K and 101.3 ± 0.7 kPa. The reliability of the experimental tie-line data was confirmed by using the Othmer–Tobias correlation. The LLE data of the ternary systems were predicted by UNIFAC method. Distribution coefficients and separation factors were evaluated for the immiscibility region.
Keywords: (Liquid + liquid) equilibria; Propionic acid; Octanol; Nonanol; Decanol; Dodecanol; UNIFAC;

(Vapour + liquid) equilibria of the {pentafluoroethane (HFC-125) + dimethyl ether (DME)} system by Jihoon Im; Gangwon Lee; Jongcheon Lee; Hwayong Kim (1510-1514).
Binary (vapour + liquid) equilibrium data were measured for the {pentafluoroethane (HFC-125) + dimethyl ether (DME)} system at temperatures from (313.15 to 363.15) K. These experiments were carried out with a circulating-type apparatus with on-line gas chromatography. The experimental data were correlated well by the Peng–Robinson Stryjek–Vera equation of state using the Wong–Sandler mixing rules.
Keywords: (Vapour + liquid) equilibria; Pentafluoroethane (HFC-125); Dimethyl ether;

Thermochemical study of two anhydrous polymorphs of caffeine by Susana S. Pinto; Hermínio P. Diogo (1515-1522).
The mean values of the standard massic energy of combustion of caffeine in phase I (or alpha) and in phase II (or beta) measured by static-bomb combustion calorimetry in oxygen, at T  = 298.15 K, are Δc u (C8H10O2N4, I) = −(21823.27 ± 0.68) J · g−1 and Δc u (C8H10O2N4, II) = −(21799.96 ± 1.08) J · g−1, respectively.The standard (p  = 0.1 MPa) molar enthalpy of formation in condensed phase for each form was derived from the corresponding standard molar enthalpies of combustion as, Δ f H m ∘ ( C 8 H 10 O 2 N 4 , cr, I ) = - ( 340.6 ± 2.3 ) kJ · mol - 1 and Δ f H m ∘ ( C 8 H 10 O 2 N 4 , cr, II ) = - ( 345.1 ± 2.3 ) kJ · mol - 1 .The difference between the standard enthalpy of formation of the two polymorphs in condensed phase was also evaluated by using reaction-solution calorimetry. The obtained result, 2.04 ± 0.25 kJ · mol−1, is in agreement, within the uncertainty, with the difference between the molar enthalpies of formation obtained from combustion experiments (4.5 ± 3.2) kJ · mol−1, which can be considered as an internal test for consistency of the results.A value for the standard enthalpy of formation of caffeine in the gaseous state was proposed: Δ f H m ∘ ( C 8 H 10 O 2 N 4 , g ) = - ( 229.7 ± 6.1 ) kJ · mol - 1 , estimated from the values of the standard enthalpies of formation of both crystalline forms obtained in this work, and the data on standard enthalpies of sublimation collected from the literature.
Keywords: Caffeine; Enthalpy of combustion; Enthalpy of formation; Differential scanning calorimetry; Solution calorimetry; Thermochemistry;

We determined apparent molar volumes V ϕ from densities measured with a vibrating-tube densimeter at 278.15 ⩽ (T/K) ⩽ 368.15 and apparent molar heat capacities C p,ϕ with a twin fixed-cell, differential, temperature-scanning calorimeter at 278.15 ⩽ (T/K) ⩽ 363.15 for aqueous solutions of N-acetyl-d-glucosamine at m from (0.01 to 1.0) mol · kg−1 and at p  = 0.35 MPa. We also determined V ϕ at 278.15 ⩽ (T/K) ⩽ 368.15 and C p,ϕ at 278.15 ⩽ (T/K) ⩽ 393.15 for aqueous solutions of N-methylacetamide at m from (0.015 to 1.0) mol · kg−1 and at p  = 0.35 MPa. Empirical functions of m and T for each compound were fitted to our results, which are then compared to those for N,N-dimethylacetamide. Estimated values of Δr V m(m,  T) and Δr C p,m(m,  T) for formation of aqueous N-acetyl-d-glucosamine from aqueous d-glucose and aqueous acetamide are calculated and discussed.
Keywords: Apparent molar volume; Apparent molar heat capacity; N-Acetyl-d-glucosamine; N-Methylacetamide;

The equilibrium pressure of ternary mixtures of {x 1CH3F +  x 2HCl +  x 3N2O} covering the entire composition range has been measured at temperature of 182.33 K by the static method. The system exhibits a minimum pressure for the binary {x 1CH3F +  x 2HCl}. The molar excess Gibbs free energy has been calculated from the experimental equilibrium pressure. For the equimolar mixture G m E ( x 1 = x 2 = x 3 = 1 / 3 ) = ( - 297 ± 20 ) J · mol - 1 . The (p,  x,  y) surface for the ternary system and the corresponding curves for the three constituent binary mixtures obtained from the Peng–Robinson equation of state are in agreement with the experimental data.
Keywords: Ternary (vapour + liquid) equilibria; Methyl fluoride; Hydrogen chloride; Nitrous oxide; Excess Gibbs free energy;

Isobaric (vapour + liquid) equilibrium (VLE) data for {2-propanol (1) + water (2) + ammonium thiocyanate (3)} were obtained at 101.3 kPa experimentally. An all-glass Fischer–Labodest type still capable of handling pressures from (0.25 to 400) kPa and temperatures up to 523.15 K was used. (Vapour + liquid) equilibrium data of (2-propanol + water) were also obtained at 101.3 kPa experimentally. An equation is proposed to fit the data of salt-containing systems using dimensionless groups called relative ratio. The proposed model was also tested for the salt-containing systems given from the literature.
Keywords: Salt-effect; (Vapour + liquid) equilibrium; 2-Propanol; Water;

Odd–even effect in melting properties of 12 alkane-α,ω-diamides by Elena Badea; Giuseppe Della Gatta; Domenico D’Angelo; Bruno Brunetti; Zuzana Rečková (1546-1552).
Fusion and solid-to-solid transitions of a homologous series of 12 linear alkane-α,ω-diamides H2NCO–(CH2)(n−2)–CONH2, where n  = (2 to 12 and 14), were investigated by differential scanning calorimetry (d.s.c.). The temperatures of fusion of even terms decreased from T fus  ≈ 572 K to about 460 K, whereas those of odd terms remained substantially constant at about 450 K. Solid-to-solid transitions were also detected for oxamide, malonamide, succinamide, adipamide, suberamide, and dodecanediamide. Regular odd–even alternation was displayed by the temperature, enthalpy, and entropy of fusion values, terms with even number of carbon atoms showing higher values than odd terms.This behaviour was attributed to different crystal packing allowing consonance between hydrogen bonding and dispersive interaction in even terms, which are characterised by multilayer structure, whereas in odd terms a strained three-dimensional network results in looser packing. Parallel alternation of densities in solid alkane-α,ω-diamides supports this interpretation. Comparison was made with literature values for temperatures, enthalpies, and entropies of fusion of isoelectronic linear alkanes, dicarboxylic acids, and alkyldiamines.
Keywords: Alkane-α,ω-diamides; Differential scanning calorimetry; Fusion; Odd–even effect; Packing pattern;

Excess volumes (V E) ultrasonic sound velocities (u), isentropic compressibilities (K s) and viscosities (η) have been measured for the binary mixtures of dimethylsulphoxide (DMSO) with 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,2,4-trichlorobenzene, o-chlorotoluene, m-chlorotoluene, p-chlorotoluene, o-nitrotoluene and m-nitrotoluene at T  = 303.15 K. The measured V E values were positive over the entire composition range in all the binary mixtures. Isentropic compressibilities (K s) have been computed for the same systems from precise sound velocity and density data. Further, deviation in isentropic compressibility (ΔK s) from ideal behaviour was also calculated. The viscosity data are analysed on the basis of corresponding states approach. Deviation in viscosities are positive over the entire composition range. The measured data is explained on the basis of intermolecular interactions between unlike molecules.
Keywords: Dilatometer; Excess volume; Interferometer; Isentropic compressibilities; Sound velocity; Viscosity; Molecular interactions;

Standard enthalpy of formation of aqueous titanyl chloride, TiOCl2(aq), at T  = 298.15 K by Melerin Madekufamba; Liliana N. Trevani; Peter R. Tremaine (1563-1567).
Enthalpies of solution of TiCl4(l) in aqueous perchloric acid have been measured in an isothermal calorimeter at T  = 298.15 K at ionic strengths of (1.964, 3.002, and 4.062) mol · kg−1. These results were extrapolated to zero ionic strength using an extended Debye–Hückel equation, to yield the standard enthalpy of solution Δ sln H m ∘ ( T = 298.15 K ) = - ( 268.03 ± 0.45 ) kJ · mol - 1 ; from which the standard partial molar enthalpy of formation of the titanyl ion was derived: Δ f H m ∘ ( TiO 2 + , aq, T = 298.15 K ) = - ( 689.4 ± 4.3 ) kJ · mol - 1 .
Keywords: Enthalpy of formation; Enthalpy of solution; Aqueous titanyl chloride; Aqueous titanyl ion;

A complete, critical evaluation of all phase diagram and thermodynamic data was performed for all phases of the (Na2SO4  + K2SO4  + Na2S2O7  + K2S2O7) system and optimized model parameters were obtained. The Modified Quasichemical Model in the Quadruplet Approximation was used for modelling the liquid phase. The model evaluates first- and second-nearest-neighbour short-range ordering, where the cations (Na+ and K+) are assumed to mix on a cationic sublattice, while anions ( SO 4 2 - , S 2 O 7 2 - ) were assumed to mix on an anionic sublattice. The Compound Energy Formalism was used for modelling the solid solutions of (Na,K)2SO4 and (Na,K)2S2O7. The models can be used to predict the thermodynamic properties and phase equilibria in multicomponent heterogeneous systems. The experimental data from the literature were reproduced within experimental error limits.
Keywords: Thermodynamic modelling; Alkali sulphate; Alkali pyrosulphate; Molten salt; Modified Quasichemical Model;

Potentiometric and ab initio studies of acid–base interactions of substituted 4-halo(Cl, Br)pyridine N-oxide systems by Łukasz Gurzyński; Aniela Puszko; Mariusz Makowski; Joanna Makowska; Lech Chmurzyński (1584-1591).
By using the potentiometric method, acidity constants have been determined in systems of tri- and tetra-substituted pyridine N-oxides. The potentiometric measurements in systems of four 4-chloropyridine N-oxide derivatives containing the chlorine atom at position 4 to the NO2 group and four bromine counterparts were carried out in polar non-aqueous solvents, viz. amphiprotic methanol (MeOH) and aprotic protophilic dimethyl sulfoxide (DMSO). It was found that in all the systems studied the pK a values were readily determinable (as indicated by small standard deviations) in MeOH, whereas in DMSO large standard deviations were obtained making the pK a values either hardly determinable or indeterminable from potentiometric measurements. Furthermore, it was demonstrated that the acidity constants of protonated N-oxides studied in MeOH changed according to the sequence of their acidity constants in water. It was also found that in the polar solvents studied, i.e. in the amphiprotic methanol and the highly basic aprotic dimethyl sulfoxide, the cationic homo-conjugation equlibrium constants could not be determined using potentiometric method. Also, by using ab initio methods at the RHF and MP2 levels and the PCM model, utilizing the Gaussian 6-31++G∗∗ basis set, energies and Gibbs free energies of the protonation reactions of the N-oxides have been determined. The energy parameters have been compared with acidity constants of the protonated N-oxides determined by potentiometric titration in methanol to establish a correlation between these approaches.
Keywords: (Acid + base) equilibria; Potentiometric titrations; ab initio Calculations; Methanol; Water; DMSO;

Apparent molar heat capacities (C P2,ϕ ), apparent molar volumes (V 2,ϕ ), and viscosities (η) of diglycine in water and in aqueous magnesium chloride (MgCl2) solutions of molality m S  ≈ (0.05 to 0.70) mol · kg−1 over the temperature range T  = (288.15 to 328.15) K have been determined using high sensitivity micro-differential scanning calorimeter, vibrating-tube digital density meter, and automatic viscosity measuring unit (AVS 350), respectively. The data have been used to calculate the partial molar heat capacities ( C P 2 ∞ ) and partial molar volumes ( V 2 ∞ ) at infinite dilution. The viscosity B-coefficients have also been obtained from viscosity data using Jones–Dole equation. The C P 2 ∞ and V 2 ∞ values of diglycine in aqueous MgCl2 solutions are higher than those in water and thus exhibit positive transfer functions ( Δ tr C P 2 ∞ and Δ tr V 2 ∞ ), which are indicative of strong interactions between diglycine and MgCl2. Corresponding viscosity B-coefficients of transfer are also generally positive. The transfer functions decrease with increase in temperature and increase with the concentration of MgCl2. The free energies, enthalpies and entropies of activation for viscous flow of diglycine in aqueous MgCl2 solutions have been obtained by using the Feakins transition-state theory. Partial molar expansibilities ( ∂ V 2 ∞ / ∂ T ) P and ( ∂ 2 V 2 ∞ / ∂ T 2 ) P at infinite dilution along with their temperature dependence, the interaction coefficients from the volume, heat capacity, and viscosity B-coefficients have been used to divulge the various kinds of plausible interactions between solute (diglycine) and cosolute (MgCl2) in solutions.
Keywords: Diglycine; Magnesium chloride; Apparent molar volumes; Apparent molar heat capacities; Viscosity; Viscosity B-coefficients; Gibbs free energy of activation; Hydration numbers;

Microcalorimetric measurements of excess enthalpies at the temperature T  = 298.15 K are reported for the binary mixture, (x 1C6H12  +  x 2C4H8O) and the two ternary mixtures {x 1C6H12  +  x 2(C4H8O or C5H10O) +  x 3(C5H12O)}. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. It is shown that good estimates of the ternary enthalpies can be obtained from the Liebermann and Fried model, using only the physical properties of the components and their binary mixtures.
Keywords: Excess enthalpy; Ternary mixture; 1-Hexene; Tetrahydrofuran; 2-Methyltetrahydrofuran; Methyl tert-butyl ether; Liebermann–Fried model;

Thermodynamic functions of α,α-trehalose dihydrate and of α,β-trehalose monohydrate at temperatures from 13 K to 300 K by Takao Furuki; Rika Abe; Hitoshi Kawaji; Tooru Atake; Minoru Sakurai (1612-1619).
Thermodynamic properties at low temperatures were investigated for α,α-trehalose dihydrate and α,β-trehalose monohydrate. The heat capacities were measured using an adiabatic calorimeter at temperatures between 13 K and 300 K. The heat capacity data were expressed as a function of temperature, T, by a polynominal of forth to sixth order, with which thermodynamic functions, enthalpy, entropy, and Gibbs free energy, were determined.
Keywords: α,α-Trehalose dihydrate; α,β-Trehalose monohydrate; Heat capacity;

In this paper, excess thermodynamic functions have been computed from the measured values of density, viscosity, and refractive index at T  = (298.15, 303.15, and 308.15) K, ultrasonic velocity at T  = 298.15 K over the entire mixture composition range of (anisole with ethanol, propan-1-ol, propan-2-ol, butan-1-ol, pentan-1-ol, or 3-methyl butan-1-ol). Excess molar volume, V E has been calculated from densities, whereas deviations in viscosity, Δη, were computed from the measured viscosities. From ultrasonic velocities, isentropic compressibilities were calculated, from which deviations in isentropic compressibility, Δk s have been computed. Lorenz–Lorentz mixture rule was used to compute molar refractivity, R from refractivity index data and from these data, deviations in molar refractivity, ΔR have been computed. Computed thermodynamic quantities have been fitted to Redlich and Kister polynomial equation to derive the coefficients and standard errors between experimental and predicted quantities. Intermolecular interactions between anisole and alkanols have been studied based on the computed excess thermodynamic quantities.
Keywords: Density; Viscosity; Refractive index; Speed of sound; Anisole; Alkanols;

Solubility of methane in water and in a medium for the cultivation of methanotrophs bacteria by Maria Celeste C. Serra; F.L.P. Pessoa; A.M.F. Palavra (1629-1633).
Solubility of methane in water and in an aqueous growth medium for the cultivation of methanotrophs bacteria was determined over the temperature range 293.15 to 323.15 K and at atmospheric pressure. The measurements were carried out in a Ben-Naim/Baer type apparatus with a precision of about ±0.3%. The experimental results were determined using accurate thermodynamic relations. The mole fractions of the dissolved gas at the gas partial pressure of 101.325 kPa, the Henry coefficients at the water vapour pressure and the Ostwald coefficients at infinite dilution were obtained. A comparison between the solubility of methane in water and those observed in fermentation medium over the temperature range of 298.15 to 308.15 K has shown that this gas is about ±2.3% more soluble in water.The temperature dependence of the mole fractions of methane was also determined using the Clarke–Glew–Weiss equation and the thermodynamic quantities, Gibbs energy, enthalpy and entropy changes, associated with the dissolution process were calculated.Furthermore, the experimental Henry coefficients for methane in water are compared with those calculated by the scaled particle theory. The estimated Henry coefficients are about ±4% lower than the experimental ones.
Keywords: Solubility; Methane; Water; Methanotrophs bacteria cultivation medium; Scaled particle theory;

(Liquid + liquid) equilibrium (LLE) data for the ternary system of (water + butyric acid + oleyl alcohol) at T  = (298.15, 308.15, and 318.15) K are reported. Complete phase diagrams were obtained by determining solubility and the tie-line data. The reliability of the experimental tie lines was confirmed by using Othmer–Tobias correlation. The UNIFAC method was used to predict the phase equilibrium data. The phase diagrams for the ternary mixtures including both the experimental and correlated tie lines are presented. Distribution coefficients and separation factors were evaluated for the immiscibility region. A comparison of the solvent extracting capability was made with respect to distribution coefficients, separation factors, and solvent-free selectivity bases for T  = (298.15, 308.15, and 318.15) K. It is concluded that oleyl alcohol may serve as an adequate solvent to extract butyric acid from its dilute aqueous solutions.
Keywords: Butyric acid; Oleyl alcohol; (Liquid + liquid) equilibria; UNIFAC;

The partial molar volumes, V 2 ∘ , and partial molar heat capacities, C p , 2 ∘ , at infinite dilution have been determined for the compounds N-acetylasparaginamide, N-acetylglutaminamide, N-acetyltyrosinamide, and N-acetyllysinamide monohydrochloride in aqueous solution at T  = (288.15, 298.15, 313.15, and 328.15) K. These results, along with the literature data for the compound N-acetylglycinamide, have been used to calculate the amino acid side-chain contributions to the thermodynamic properties. These side-chain contributions are compared with those obtained using small peptides as side-chain model compounds.
Keywords: Partial molar volume; Partial molar heat capacity; N-Acetyl amino acid amides; Amino acid side-chain contributions; Group additivity; Aqueous solution;

The vapour pressure of binary mixtures of hydrogen sulphide with ethane, propane, and n-butane was measured at T  = 182.33 K covering most of the composition range. The excess Gibbs free energy of these mixtures has been derived from the measurements made. For the equimolar mixtures G m E ( x 1 = 0.5 ) = ( 835.5 ± 5.8 ) J · mol - 1 for (H2S + C2H6), (820.1 ± 2.4) J · mol−1 for (H2S + C3H8), and (818.6 ± 0.9) J · mol−1 for (H2S +  n-C4H10). The binary mixtures of H2S with ethane and with propane exhibit azeotropes, but that with n-butane does not.
Keywords: (Vapour + liquid) equilibria; Hydrogen sulphide; Ethane; Propane; n-Butane; Excess Gibbs free energy;

A small-scale adiabatic calorimeter has been constructed as part of a larger project to study the thermodynamics of nanomaterials and to facilitate heat capacity measurements on samples of insufficient quantity to run on our current large-scale adiabatic apparatus. This calorimeter is designed to measure the heat capacity of samples whose volume is less than 0.8 cm3 over a temperature range of T  = 13 K to T  = 350 K. Heat capacity results on copper, sapphire, and benzoic acid show the accuracy of the measurements to be better than ±0.4% for temperatures higher than T  = 50 K. The reproducibility of these measurements is generally better than ±0.25%.
Keywords: Heat capacity; Adiabatic calorimetry; Calorimetric standards;

Densities and viscosities of the binary mixtures of 2,4,6-trimethyl-1,3,5-trioxane with methyl acetate, ethyl acetate, and 1-butyl acetate were measured over the entire mole fractions at (298.15, 303.15, and 308.15) K. Using the experimental values of densities ρ and viscosities η, excess molar volumes V E, viscosity deviations δη were calculated. The values of excess molar volumes V E and viscosity deviations δη were fitted to the Redlich–Kister polynomial.
Keywords: Molecular interactions; 2,4,6-Trimethyl-1,3,5-trioxane; Excess molar volumes; Viscosity deviations; Redlich–Kister polynomial;

(Liquid + liquid) equilibrium (LLE) data for the {water + acetic acid + dibasic esters mixture (dimethyl adipate + dimethyl glutarate + dimethyl succinate)} system have been determined experimentally at T  = (298.2, 308.2, and 318.2) K. Complete phase diagrams were obtained by determining solubility curve and tie-line data. The reliability of the experimental tie-line data was confirmed by using the Othmer–Tobias correlation. The UNIFAC model was used to predict the phase equilibrium in the system using the interaction parameters determined from experimental data between CH2, CH3COO, CH3, COOH, and H2O functional groups. Distribution coefficients and separation factors were compared with previous studies.
Keywords: (Liquid + liquid) equilibria; Acetic acid; Environmentally friendly solvents; Dibasic esters mixture; UNIFAC;

Densities, viscosities, and ultrasonic velocities of binary mixtures of trichloromethane with methanol, ethanol, propan-1-ol, and butan-1-ol have been measured over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure. From the experimental values of density, viscosity, and ultrasonic velocity, the excess molar volumes (V E), deviations in viscosity (Δη), and deviations in isentropic compressibility (Δκ s) have been calculated. The excess molar volumes, deviations in viscosity and deviations in isentropic compressibility have been fitted to the Redlich–Kister polynomial equation. The Jouyban–Acree model is used to correlate the experimental values of density, viscosity, and ultrasonic velocity.
Keywords: Excess molar volumes; Deviations in viscosity; Deviations in isentropic compressibility; Trichloromethane; Methanol; Ethanol; Propan-1-ol; Butan-1-ol;

Speed of sound and density values for ternary systems (amino acid + salt + water): l-isoleucine/l-proline/l-glutamine in aqueous solutions of 1.5 M KCl, 1 M KNO3, and 0.5 M K2SO4 have been measured for several concentrations of amino acids at different temperatures (303.15, 308.15, 313.15, 318.15, and 323.15 K). Using speed of sound and density data, the thermodynamic parameters such as isentropic compressibility (κ s), change in isentropic compressibility (Δκ s) and relative change (Δκ s/κ 0) in isentropic compressibility have been computed. The isentropic compressibility values decrease with increase in the amino acid concentration as well as with temperature. The decrease in κ s values with increase in concentration of l-isoleucine/l-proline/l-glutamine in 1.5 M KCl, 1 M KNO3, and 0.5 M K2SO4 has been ascribed to an increase in the number of incompressible zwitterions in solutions, and the formation of ‘zwitterions–ions’ and ‘zwitterions–water dipole’ entities in solutions. The decrease in κ s values with increase in temperature has been attributed to the corresponding decrease of κ relax (a relaxational part of compressibility), which is dominant over the corresponding increase of κ (an instantaneous part of compressibility). The trends of variation of Δκ s and Δκ s/κ 0 with variations in solute concentration and temperature have also been discussed in terms of solute–solute and solute–solvent intermolecular/interionic interactions operative in the systems.
Keywords: l-Isoleucine; l-Proline; l-Glutamine; KCl; KNO3; K2SO4; Isentropic compressibility; Zwitterions–ions interactions;

(Vapor + liquid) equilibria of the binary mixtures of m-cresol with C1–C4 aliphatic alcohols at 95.5 kPa by T.E. Vittal Prasad; N. Anil Kiran; N. Malleswara Reddy; D.H.L. Prasad (1696-1700).
Bubble point temperatures at 95.5 kPa, over the entire composition range, are measured for the binary mixtures formed by m-cresol with: methanol, ethanol, 1-propanol, 2-propanol, and n-, iso-, sec-, and tert-butanols – using a Swietoslawski-type ebulliometer. The liquid phase composition – bubble point temperature measurements are well represented by the Wilson model. (Vapor + liquid) equilibria predicted from the model are presented.
Keywords: Bubble point temperatures; m-Cresol; Aliphatic alcohols; (Vapor + liquid) equilibria;

Heat capacity and standard molar enthalpy of formation of crystalline 2,6-dicarboxypyridine (C7H5NO4) by Quan Shi; Zhi-Cheng Tan; You-Ying Di; Xue-Chuan Lv; Bo Tong; Zhi-Heng Zhang; Li-Xian Sun; Tao Zhang (1701-1705).
Low-temperature heat capacity C p,m of 2,6-dicarboxypyridine (C7H5NO4; CAS 499-83-2) was precisely measured in the temperature range from (80 to 378) K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The thermodynamic functions [H T  −  H 298.15] and [S T  −  S 298.15] were calculated in the range from (80 to 378) K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined, Δ c H m ∘ ( C 7 H 5 NO 4 , cr ) = - ( 2741.41 ± 0.49 ) kJ · mol - 1 and Δ f H m ∘ ( C 7 H 5 NO 4 , cr ) = - ( 727.74 ± 1.50 ) kJ · mol - 1 , by means of a precision oxygen-bomb combustion calorimeter at T  = 298.15 K. The thermodynamic properties of the compound were further investigated through differential scanning calorimeter (DSC) and the thermogravimetric (TG) analysis.
Keywords: 2,6-Dicarboxypyridine; Heat capacity; Thermodynamic function; Adiabatic calorimetry; Standard molar enthalpy of combustion; Standard molar enthalpy of formation; TG-DTA; DSC;

Thermodynamic properties of the gaseous barium silicates BaSiO2 and BaSiO3 by S.I. Lopatin; S.M. Shugurov; V.L. Stolyarova; Z.G. Turnina (1706-1710).
In the present study, the stability of gaseous barium silicates was confirmed by the high temperature mass spectrometry. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined for gaseous barium silicates as (−510 ± 15) kJ · mol−1 and (−884 ± 18) kJ · mol−1 at 298 K; standard atomization enthalpies as (1637 ± 17) kJ · mol−1 and (2318 ± 20) kJ · mol−1 at 298 K for BaSiO2 and BaSiO3, respectively. Based on the results obtained the critical analysis of the literature data was carried out.
Keywords: Gaseous oxyacid salts; Barium silicates; BaSiO2(g); BaSiO3(g); Knudsen cell/mass spectrometry; Thermodynamic functions;

Critical parameters for isobutane determined by the image analysis by G. Masui; Y. Honda; M. Uematsu (1711-1716).
(p,  ρ,  T) Measurements and visual observations of the meniscus for isobutane were carried out carefully in the critical region over the range of temperatures: −15 mK ⩽ (T  −  T c) ⩽ 35 mK, and of densities: −7.5 kg · m−3  ⩽ (ρ  −  ρ c) ⩽ 7.5 kg · m−3 by a metal-bellows volumometer with an optical cell. Vapor pressures were also measured at T  = (310, 405, 406, 407, and 407.5) K. The critical point of T c and ρ c was determined by the image analysis of the critical opalescence which is proposed in this study. The critical pressure p c was determined to be the pressure measurement at the critical point. Comparisons of the critical parameters with values given in the literature are presented.
Keywords: Critical parameters; Image analysis; Isobutane; (p,  ρ,  T) Measurements; Vapor pressure;

Experimental data on density, viscosity, and refractive index at T  = (298.15, 303.15, and 308.15) K, while speed of sound values at T  = 298.15 K are presented for the binary mixtures of (methylcyclohexane + benzene), methylbenzene (toluene), 1,4-dimethylbenzene (p-xylene), 1,3,5-trimethylbenzene (mesitylene), and methoxybenzene (anisole). From these data of density, viscosity, and refractive index, the excess molar volume, the deviations in viscosity, molar refraction, speed of sound, and isentropic compressibility have been calculated. The computed values have been fitted to Redlich–Kister polynomial equation to derive the coefficients and estimate the standard errors. Variations in the calculated excess quantities for these mixtures have been studied in terms of molecular interactions between the component liquids and the effects of methyl and methoxy group substitution on benzene ring.
Keywords: Excess molar volume; Deviations in viscosity; Molar refraction; Speed of sound; Isentropic compressibility; Methylcyclohexane; Aromatic hydrocarbons; Molecular interactions;

In this paper, the azeotropic behaviour of the (benzene + cyclohexane + chlorobenzene) ternary mixture was experimentally investigated with the aim of enhancing the knowledge for the feasible use of chlorobenzene as an entrainer for the azeotropic distillation of the binary azeotrope. Such a study has not been reported in the literature to the best of the authors’ knowledge. (Vapour + liquid) equilibria data for (benzene + cyclohexane + chlorobenzene) at 101.3 kPa were obtained with a Othmer-type ebulliometer. Data were tested and considered thermodynamically consistent. The experimental results showed that this ternary mixture is completely miscible and exhibits an unique binary homogeneous azeotrope, an unstable node at the conditions studied, and the propitious topological characteristics (residual curve map and relative volatility) to be separated. Satisfactory results were obtained for the correlation of equilibrium compositions with the UNIQUAC activity coefficients model and also for prediction with the UNIFAC method. In both cases, low root mean square deviations of the vapour mole fraction and temperature were calculated. The capability of chlorobenzene as a modified distillation agent at atmospheric condition is discussed in terms of the thermodynamic topological analysis. A conceptual distillation scheme with reversed volatility is proposed to separate the azeotropic mixture. In order to reduce the operational cost requirements of the sequence of columns proposed, the range for optimal reflux and the ratio for feed flow conditions were studied.
Keywords: Phase; Equilibria; Prediction; Thermodynamic topological analysis; Azeotrope; Benzene; Cyclohexane; Chlorobenzene; Entrainer;