Excess Molar Enthalpies Research Articles

Steric and electronic effects to interpret non-covalent interactions in binary mixtures of dimethyl carbonate and isomeric cresols through thermophysical, acoustic and spectroscopic studies

The densities (ρ), viscosities (η) and ultrasonic velocities (u) were measured for the binary mixtures of dimethyl carbonate (DMC) and isomeric cresols viz., o-cresol, m-cresol, p-cresol over the entire range of composition at atmospheric pressure and at different temperatures (303.15, 308.15,313.15, 318.15) K. From these experimental results, excess molar volume $$(V_{\text{m}}^{\text{E}} )$$ , deviation in adiabatic compressibility (Δβ ad), excess intermolecular free length ( $$L_{\text{f}}^{\text{E}}$$ ), excess acoustic Impedance (Z E), deviation in viscosity (Δη), excess Gibbs free energy of activation of viscous flow $$\left( {\Delta G^{{*{\text{E}}}} } \right)$$ and excess enthalpy ( $$H^{\text{E}}$$ ) have been calculated. The excess or deviation properties were fitted to Redlich–Kister polynomial equation to obtain their coefficients and standard deviations. The excess or deviation properties were found to be either negative or positive depending on the molecular interactions between the components of hetero molecules, and the nature of liquid mixtures has been discussed in terms of molecular interactions through steric and electronic effects. To know more about solute–solvent interactions, partial molar volumes ( $$\bar{V}_{{{\text{m}},1}} ,\bar{V}_{{{\text{m}},2}}$$ ) and excess partial molar volumes ( $$\bar{V}_{{{\text{m}},1}}^{\text{E}} , \bar{V}_{{{\text{m}},2}}^{\text{E}}$$ ) have been computed. Further, variation of excess molar enthalpy with pressure is also evaluated to elucidate the molecular interactions in the liquid mixture. The present investigation also comprises of evaluation of the acoustic nonlinearity parameter (B/A) in the mixtures and calculation of cohesive energy (ΔA), Van der Wall’s constants (a, b), distance of closest approach (d). The FTIR provides support to the thermodynamic findings to explain specific interaction between unlike molecules.

Separation of binary mixtures hexane/hex-1-ene, cyclohexane/cyclohexene and ethylbenzene/styrene based on limiting activity coefficients

The measurements of a limiting activity coefficients, γ13∞ at infinite dilution for 63 solutes including wide spectra of alkanes, alkenes and alkynes as well as aromatic hydrocarbons, alcohols, water, ethers, ketones, acetonitrile, pyridine, 1-nitropropane, thiophene, and esters in the 1-(3-hydroxypropyl)pyridinium dicyanamide, [N-C3OHPY][DCA], determined by gas-liquid chromatography at temperature range of (298.15–368.15)K are developed. The synthesis and thermochemical characteristic of the ionic liquid (IL) is described. The density and viscosity of the IL was measured as a function of temperature in a range of (298.15–368.15) K. The comparison of γ13∞ for selected solutes in ionic liquids (ILs) with [N-C3OHPY]+ cation and [TCM]−, [DCA]−, [TCB]− and [SCN]−-anions at one temperature, T=328.15K is shown. The gas-liquid partition coefficients, KL at infinite dilution and the limiting fundamental thermodynamic functions, the partial molar excess Gibbs energy, enthalpy and entropy were calculated for all solutes. The values of selectivity and capacity for three separation problems hexane/hex-1-ene, cyclohexane/cyclohexene and methylbenzene/styrene were calculated from γ13∞ and compared to literature values for [N-C3OHPY]-based or [DCA]-based ILs for the same separation problems. The data presented here shows that [N-C3OHPY][DCA] reveals large selectivity 2.34, 2.79 and 2.27 in three of discussed separation problems. However, the comparison to the measured earlier [DCA]-based ILs shows the low capacity for the hex-1-ene and cyclohexene. The Abraham solvation parameter model was also presented for all solutes. On the bases of the results the intermolecular interactions of the chosen IL and solutes was discussed.

Relevance of the thermodynamic ERAS model for liquid mixtures with components exhibiting a small degree of self-association

The thermodynamic extended real associated solution (ERAS) model is reviewed and modified to accommodate weakly associating components. ERAS is a theoretical scheme applied to binary liquid mixtures whereby certain physically meaningful parameters such as the association equilibrium constants, species reduced volume and energy terms may be determined by optimization against the experimental excess molar volumes and enthalpies. The implicit assumption used for any non-associating molecule B is to routinely set the hydrogen-bonding energy ΔhB*, reaction volume ΔvB* and association constants KB to zero. It is proven here that such assignments lead to singularities in the ERAS parameters that are featured in the excess state functions used. A series of optimizations using the results of conductor-like screening model for real solvents (COSMO-RS) on the excess enthalpy HE of dimethoxymethane in binary mixtures with a series of alcohols are determined, and the parameters ΔhB*, ΔhAB* (mixed enthalpy of reaction) and XAB (interaction parameter) are determined. It is shown that the stipulated range of XAB values from ERAS theory requires minor modification if the above assumptions are not made. The magnitude of the computed variables are shown to be physically reasonable. The Bondi group averaged estimates for si, the ratio of the van der Waals (vdW) surface area to the vdW volume for molecule i, are contrasted against the more specific and reliable derivations from quantum calculations when calculating the excess functions. The degree of correlation is improved using the latter si values. We conclude that the results of the optimizations indicate that the ERAS model can be extended even to weakly self-associating components previously considered impossible in especially engineering thermodynamical applications, with the above modifications and refinements.

The study of physico-chemical properties of binary systems consisting of N-Methylcyclohexylamine with 2-alkanols at T = (298.15–328.15) K

In this work, densities, ρ and refractive indices, nD of N-Methylcyclohexylamine+2-alkanols have been measured over the entire range of composition at four temperatures 298.15, 308.15, 318.15 and 328.15K and ambient pressure (81.5kPa), using Anton Paar DMA 4500 oscillating densimeter and Anton Paar Abbemat 500 automatic refractometer. From experimental data, excess molar volumes, VmE, partial molar volumes, V‾‾i, apparent molar volumes, Vϕi, thermal expansion coefficients, α, excess thermal expansion coefficients, αE, isothermal coefficients of excess molar enthalpy, (∂HmE/P)T,x, and refractive index deviations, ΔnD, have been calculated for binary systems consisting of N-Methylcyclohexylamine+2-alkanols (2-propanol, 2-butanol, 2-pentanol, 2-hexanol, 2-heptanol and 2-octanol). The excess molar volumes, VmE, and refractive index deviations, ΔnD were correlated with the Redlich–Kister polynomial equation. The effect of temperature and chain length of alcohol on the excess molar volumes and refractive index deviations are discussed in terms of molecular interaction between unlike molecules. The excess molar volumes were negative and refractive index deviations were positive over the entire composition range and were plotted against the mole fraction of 2-alkanols over the entire composition range. Negative excess molar volumes and positive refractive index deviations indicate the strong hydrogen bonding between unlike molecules of mixtures. A comparative study has been made of the refractive indices obtained experimentally and those calculated by means of the Lorentz–Lorenz, Gladstone–Dale, Weiner and Arago–Biot relations.

Thermodynamic properties of mixtures containing 1-butyl-2,3-dimethylimidazolium tetrafluoroborate and cyclopentanone or cyclohexanone

The densities, ρ, speeds of sound, u, and molar heat capacities, CP, of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (1) + cyclopentanone or cyclohexanone (2) mixtures at 293.15, 298.15,303.15 and 308.15 K and excess molar enthalpies, HE of same mixtures at 298.15 K have been measured as a function of composition. The observed ρ, u, and CP values are used to determine excess molar volumes, VE, excess isentropic compressibilities, κSE and excess heat capacities, CPE. The analysis of VE data in terms of Graph theory has suggested that while 1-butyl-2,3-dimethylimidazolium tetrafluoroborate exists as monomer; cyclopentanone and cyclohexanone exist as mixture of open and cyclic dimer. The analysis of inter-nuclear distances among interacting atoms (predicted by quantum mechanical calculations) also supports the presence of proposed molecular entities in pure and mixed states. It has been observed that VE, κSE, CPE and HE estimated by Graph theory compare well with their experimental values.

Thermodynamic Studies of Molecular Interactions in Mixtures Containing Tetrahydropyran, 1,4-Dioxane, and Cyclic Ketones

The densities ρ, speeds of sound u, and molar heat capacities CP of tetrahydropyran or 1,4-dioxane (1) + cyclohexanone or cycloheptanone (2) mixtures at 293.15, 298.15, 303.15, and 308.15 K, and excess molar enthalpies, HE at 308.15 K and atmospheric pressure 0.1 MPa have been measured over the entire composition range. The excess molar volumes VE, excess isentropic compressibilities κSE, and excess heat capacities, CPE of the studied mixtures have been determined using the measured experimental data. The observed VE, κSE, HE, and CPE data have been tested in terms of graph theory. The analyses of VE data by graph theory suggest that while tetrahydropyran or 1,4-dioxane exists as a mixture of monomer and dimer; cyclohexanone or cycloheptanone exists as a mixture of open and cyclic dimer. Further, (1 + 2) mixtures are characterized by interactions between oxygen atom/s and hydrogen atom of tetrahydropyran or 1,4-dioxane with hydrogen atom/s and oxygen atom of cyclohexanone or cycloheptanone. The quantum mechanical calculations and analysis of IR spectral data of (1 + 2) mixtures also support this viewpoint. It has been observed that graph theory correctly predicts the VE, κSE, HE, and CpE data of the present mixtures.

Excess molar enthalpies of ethane-1,2-diamine plus primary and secondary alkanols (C1–C4) and correlation with Redlich-Kister, Wilson, NRTL and UNIQUAC models at T = 298 K

Excess molar enthalpies, HmE of binary mixtures of ethane-1,2-diamine (EDA) with methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol were calculated from calorimetric data at T=298K and atmospheric pressure (81.5kPa) with a Parr 1455 solution calorimeter. All the binary mixtures showed exothermic behavior over the entire range of compositions. From the experimental results, the excess partial molar enthalpies, HiE and excess partial molar enthalpies at infinite dilution, HiE,∞ were calculated. Excess molar enthalpies, HmE values increase as the chain length of the alkanol is increased, showing minimum values varying from −4395 (methanol) to −1987 J·mol-1 (butan-2-ol). The minimum HmE values were observed about 0.4mol fraction of ethane-1,2-diamine (EDA). The experimental results were discussed in terms of intermolecular interactions, particularly hydrogen-bonding interactions between like and unlike molecules. Finally the experimental results were correlated by the Redlich–Kister equation and the three thermodynamic models (Wilson, NRTL, and UNIQUAC) based on the local composition theory.

Excess molar enthalpies of dichloromethane +acetone or + dimethyl sulfoxide or + tetrahydrofuran or + 1, 4-dioxane at the temperature 313.15 K

Excess molar enthalpies HE at T= 313.15 K have been determined for dichloromethane (CH2Cl2) + acetone (CH3)2CO or + dimethyl sulfoxide (CH3)2SO) (DMSO) or + tetrahydrofuran (C4H8O) or + 1, 4-dioxane (C4H8O2). The excess molar enthalpies for all systems are exothermic in nature. The excess partial molar enthalpies of the components HEm, 1, and HEm, 2 were calculated from HE data. These results indicate the existence of specific interactions between all these components.

Influence of temperature on thermodynamics for binary mixtures of short aliphatic protic ionic liquids

Two binary mixtures of protic ionic liquids comprising formate, acetate and propionate anions and 2-hydroxyethyl ammonium, bis(2-hydroxyethyl) ammonium and tris(2-hydroxyethyl) ammonium cations have been studied in terms of volumetric and acoustic properties as a function of temperature. The corresponding derived properties have been computed from the experimental data and fitted to temperature dependent Redlich?Kister and Redlich? ?Mayer equations; accurate results being obtained. Other properties such as intermolecular free length, acoustic impedance, geometrical volume, collision factor and isothermal coefficient of pressure excess molar enthalpy were computed due to their importance in the study of specific molecular interactions. The new experimental data were used to test the prediction capability of different models for density (Mchaweh?Nasrifar?Moshfeghian (MNM) model and the modified Heller temperature dependent equation (MHE)) and ultrasonic velocity (different empirical equations, collision factor theory (CFT) and free length theory (FLT)). The high non-ideality of these mixtures points to strong contractive behaviour at any temperature and composition. The obtained results indicate that ionic liquid interactions into mixture are stronger than in the ionic pure components for both mixtures at any studied condition. Despite the strong ion interaction, the tested models showed, at least, the qualitative prediction capability.

Thermodynamic properties of five biofuel-relevant compounds at infinite dilution in water

In this work, thermodynamic behavior of five biomass-derived compounds, namely furfural, 2-methylfuran, 2,5-dimethylfuran, methyl vinyl ketone, and allyl alcohol, in highly dilute aqueous solutions has been experimentally investigated. Using the inert gas stripping technique, their air-water partition coefficients (Kaw) and limiting activity coefficients γ1∞ were measured at several temperatures in the range from (273 to 333) K. Except for the furans, infinite dilution partial molar excess enthalpies and volumes were further determined as functions of temperature from (288 to 318) K by tandem flow mixing calorimetry and vibrating-tube densimetry, which in turn allowed reliable derivation of respective heat capacities and expansivities. In addition, densities of all five pure liquids and viscosities of furfural and allyl alcohol were also measured in the range from (288 to 318) K. For each compound, the vapor-liquid equilibrium and (when measured) calorimetric data of this work together with some relevant data reported previously in the literature were simultaneously correlated by a three-parameter model equation providing adequate simultaneous description of all information involved. As a result, recommended thermodynamically consistent temperature dependences of Kaw and γ1∞ of superior accuracy were thus established in the range from the melting point to the normal boiling point of water. The variation of Kaw and γ1∞ with temperature and solute molecular structure along with related energetic functions of dissolution and hydration of the examined compounds were overviewed and briefly discussed.

Separation of binary mixtures based on gamma infinity data using [EMIM][TCM] ionic liquid and modelling of thermodynamic functions

The measurements of activity coefficients γ13∞ at infinite dilution for 64 solutes including water is presented for 1-ethyl-3-methylimidazolium tricyanomethanide, [EMIM][TCM] ionic liquid (IL). The data obtained by gas-liquid chromatography at six temperatures at 10K intervals in range of (318.15 to 368.15) K are presented for non-polar and polar solutes as alkanes, alkenes and alkynes as well as aromatic hydrocarbons, alcohols, water, ethers, ketones, acetonitrile, pyridine, 1-nitropropane, thiophene, and esters. The comparison of γ13∞ at one temperature, T=328.15K for selected solutes in ionic liquids (ILs) with [EMIM]+ cation and [TCM]−, [DCA]−, [TCB]− and [SCN]− -anions is presented. The gas-liquid partition coefficients, KL at infinite dilution and the fundamental thermodynamic functions, the partial molar excess Gibbs energy, enthalpy and entropy at infinite dilution are calculated for all solutes. The values of selectivity and capacity for three separation problems such as hexane/hex-1-ene, cyclohexane/cyclohexene and methylbenzene/styrene are calculated from γ13∞ and compared to literature values for [EMIM]-based or [TCM]-based ILs for the same separation problems. The data presented here shows that [EMIM][TCM] reveals large selectivity 2.35, 2.24, and 2.01 in three of discussed separation problems, hexane/hex-1-ene, cyclohexane/cyclohexene and ethylbenzene/styrene. The comparison to the measured earlier [TCM]-based ILs shows the lowest capacity for the hexane/hex-1-ene separation problem. The Abraham solvation parameter model is also discussed. Present study discusses the intermolecular interactions of the chosen IL and solutes and may be of considerable importance for selection of optimum entrainer for the desired three separation processes.

Excess Molar Enthalpies of Deep Eutectic Solvents (DESs) Composed of Quaternary Ammonium Salts and Glycerol or Ethylene Glycol

Molar enthalpies of mixing (HE) were measured for the following deep eutectic solvents (DESs): {choline chloride + glycerol}, {choline chloride + ethylene glycol}, {tetrabutylammonium chloride + glycerol}, and {tetrabutylammonium chloride + ethylene glycol} at 323.15 K and molar ratios of 1:4, 1:3, 1:2 and 1:1. Results show that all systems are endothermic, with HE values ranging from 1.90 to 5.35 kJ·mol–1. Results indicate that the intermolecular interactions between the molecules of the pure components are stronger than those of the DESs complexes. To shed some light on the mutual interactions between the molecules within the mixtures, effects of the hydrogen bond acceptor structure (HBA), hydrogen bond donor structure (HBD), and concentration (HBA:HBD molar ratio) were analyzed. The nature of the HBA salt is the most important: choline chloride-based systems required almost twice as much energy as tetrabutylammonium chloride-based systems in order to form the DES mixture, most likely because of a highe...

Excess enthalpies of ternary mixtures of (oxygenated additives + cycloalkane) in fuels and bio-fuels: (dibutyl ether + 1-propanol + cyclohexane), or methylcyclohexane, at T = (298.15 and 313.15) K

New experimental excess molar enthalpy data of the ternary systems (dibutyl ether+1-propanol+cyclohexane), or methylcyclohexane, and the corresponding binary systems at T=(298.15 and 313.15)K at atmospheric pressure are reported. A quasi-isothermal flow calorimeter has been used to make the measurements. All the binary and ternary systems show endothermic character at both temperatures. The experimental data for the systems have been fitted using the Redlich–Kister rational equation and the UNIQUAC model.

A green process for recovery of 1-propanol/2-propanol from their aqueous solutions: Experimental and MD simulation studies

In the present study, we have found that a common and relatively inexpensive biological buffer tris(hydroxymethyl)aminomethane (TRIS) is potentially applicable to shift the azeotrope compositions of aqueous solutions of 1-propanol and 2-propanol. By taking the advantage of our findings, we are proposing a green process for the recovery of these organics from their respective aqueous solutions. In order to confirm the effect of TRIS buffer on vapor–liquid equilibrium behavior of the aqueous propanol systems, we measured the isobaric vapor–liquid equilibrium (VLE) data at 101.3kPafor the 1-proponol+water+TRIS and 2-propanol+water+TRIS systems over the azeotropic range with various concentrations of TRIS (0.02, 0.04, 0.08, and 0.12 in mole fraction). The binary interaction parameters were obtained for TRIS with water, TRIS with 1-propanol, and TRIS with 2-propanol by correlating the new VLE data with the NRTL model. The isobaric VLE properties for the investigated propanol+water mixtures in the presence of various concentrations of TRIS were also predicted with the conductor-like screening model COSMO-RS. Based on the predicted excess molar enthalpies (HEm) from the COSMO-RS, the interactions between all constituent pairs of molecules were estimated. To explore the mechanism of TRIS-based separation of 1-propanol/2-propanol from their aqueous solutions, the interactions between different pairs of molecules were also investigated by using fluorescence analysis and Molecular Dynamic (MD) simulation. In comparison with the conventional corrosive inorganic salts and volatile organic entrainers, TRIS is non-corrosive, non-volatile, and almost totally recyclable. With the aid of TRIS, a cleaner separation process is proposed in the present study for recovery of 1-propanol and 2-propanol from their aqueous solutions based on buffer-swing distillation.

The effect of 2,2,2-trifluoroethanol on water studied by using third derivatives of Gibbs energy, G

We determined the excess partial molar enthalpy and the excess partial molar volume, HTFEE, VTFEE, of 2,2,2-trifluoroethanol (TFE) in TFE-H2O at 25.0°C. We then evaluate the TFE-TFE interactions in terms of enthalpy and volume, HTFE-TFEE and VTFE-TFEE, graphically without resorting to any model dependent fitting functions. Both model-free third derivatives indicate that TFE is a hydrophobic solute and that as other hydrophobic alkyl mono-ols there are three distinct mixing schemes, Mixing Schemes I, II, and III in their aqueous solutions. The relative strength in hydrophobicity between TFE and tert-butylalcohol (TBA), for example, gave a mixed message within the behavior of these third derivative quantities. We thus applied the 1-propanol (1P) probing methodology (Koga, Y. Phys. Chem. Chem. Phys. 2013, 15, 14548) that utilizes the fourth derivative in effect, and quantified the degree of hydrophobicity of TFE. It turned out that TFE is a stronger hydrophobe than 1P and ethanol (ET), and has approximately the same hydrophobicity as TBA within the estimated uncertainty. These findings were compared with the ability reported in literature to denature β-lactoglobulin and to induce α-helices in melittin in their aqueous solutions.

Topological analysis of thermodynamic properties of binary mixtures containing 1-butyl-3-methylimidazolium tetrafluoroborate and cycloalkanones

This work presents densities, ρ, speeds of sound, u, and molar heat capacities, Cp, of 1-butyl-3-methylimidazolium tetrafluoroborate (1) + cyclopentanone or cyclohexanone (2) mixtures as a function of composition at 293.15, 298.15, 303.15, 308.15 K and excess molar enthalpies, HE of same mixtures at 298.15 K. The measured ρ, u and Cp values were used to calculate excess molar volumes, VE, excess isentropic compressibilities, \(\kappa_{\text{S}}^{\text{E}}\) and excess heat capacities, \(C_{\text{P}}^{\text{E}}\). The VE, \(\kappa_{\text{S}}^{\text{E}}\), HE and \(C_{\text{P}}^{\text{E}}\) have been tested in terms of Graph theory. The analysis of VE data and IR spectroscopic data has suggested that (1 + 2) mixtures are characterized by interactions between hydrogen and oxygen atom of cyclopentanone or cyclohexanone with fluorine atom of [BF4]− anion and proton of –CH3 group attached to imidazolium ring of [Bmim]+ cation. The quantum mechanical calculations also support the proposed molecular entities in pure as well as mixed states along with observations inferred from IR data of the studied mixtures. The VE, \(\kappa_{\text{S}}^{\text{E}}\), HE and \(C_{\text{P}}^{\text{E}}\) values estimated by Graph theory are in agreement with experimental values.

Topological investigations of mixtures containing cyclic ether and cyclic alkanones

Excess molar volumes, VE, excess isentropic compressibilities, κSE, excess heat capacities, CPE of 1,3-dioxolane (1)+cyclohexanone or cycloheptanone or N-methylpyrrolidin-2-one (2) mixtures have been determined using measured densities ρ, speeds of sound, u and molar heat capacities, CP over the entire composition range at 293.15, 298.15, 303.15 and 308.15K. The excess molar enthalpies, HE of the present mixtures have been measured at 308.15K. The analysis of VE, κSE, HE and CPE data (in terms of Graph theory), IR spectral data and quantum mechanical calculations of the studied mixtures suggest that (i) 1,3-dioxolane exists as a mixture of monomer and dimer; cyclohexanone, cycloheptanone exist as mixture of open and cyclic dimer; N-methylpyrrolidin-2-one exists as dimer (ii) 1,3-dioxolane (1)+cyclohexanone or cycloheptanone (2) mixtures are characterized by interactions among the hydrogen and oxygen atoms of the 1,3-dioxolane with the oxygen and hydrogen atoms of cyclohexanone or cycloheptanone respectively; (iii) in 1,3-dioxolane (1)+N-methylpyrrolidin-2-one (2), there are interactions between the oxygen atoms of 1,3-dioxolane with the oxygen and nitrogen atom of N-methylpyrrolidin-2-one. The VE, κSE, HE and CPE values calculated by Graph theory are consistent with experimental values.

Partial molar enthalpies of organic solutes in the ionic liquid [EMIM][EtSO4

Partial molar excess enthalpies of mixing of the organic liquids methanol, acetonitrile, acetone and propan-1-ol in 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]) have been measured using a titration calorimeter. Data have been obtained at 298K, in the case of methanol also at 308K, in the mole fraction range of the organic liquid x2 from 0.005 to 0.05. The results have been extrapolated to infinite dilution for determining enthalpies of dilution at infinite concentrations H¯2,∞E (x2=0). Alternatively values of H¯2,∞E can be obtained from measurements of activity coefficients γ2∞ at different temperatures using the gas chromatographic or the dilutor technique. However, according to our error analysis calorimetric results of H¯2E,∞ are by a factor 2–3 more reliable than the results obtained by the indirect methods.

Use of HS-SPME for analysis of the influence of salt concentration and temperature on the activity coefficient at infinite dilution of ethanol-water-salt systems

Accurate knowledge of thermodynamic properties is of great importance in optimizing industrial processes of chemical separation. However, traditional techniques have limitations that hinder the use in complex systems, especially involving strong electrolytes. Solid phase micro-extraction (SPME) was used to determine infinite dilution activity coefficients of ethanol in water-salt systems. Different concentrations of inorganic salts were used to verify the influence on the activity coefficient at temperatures of 323.15, 333.15, 343.15, and 353.15 K. Salts evaluated in SPME include potassium chloride (KCl), calcium chloride (CaCl2), and aluminum chloride (AlCl3) at concentrations of 1.125, 1.800, and 2.571 mol/Kg. Comparisons between data obtained using SPME and the theoretical basis and literature data showed good agreement. Thermodynamic parameters such as partial molar excess enthalpy at infinite dilution, partial molar excess entropy at infinite dilution, and partial molar excess Gibbs energy were calculated from the infinite dilution activity coefficient. AlCl3 produced the highest activity coefficient for ethanol at infinite dilution, indicating a strong influence on the separation of ethanol. The results obtained indicate that SPME technique can be considered an alternative method on determination of activity coefficients at infinite dilution.

Topological investigations of molecular interactions in binary ionic liquid mixtures with a common ion: Excess molar volumes, excess isentropic compressibilities, excess molar enthalpies and excess molar heat capacities

The densities, ρ, speeds of sound, u, and molar heat capacities, CP, of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i)+ 1-butyl-3-methylimidazolium tetrafluoroborate (j); 1-butyl-3-methylimidazolium tetrafluoroborate (i)+1-ethyl-3-methylimidazolium tetrafluoroborate (j) and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i)+1-ethyl-3-methylimidazolium tetrafluoroborate (j) mixtures at temperatures (293.15, 298.15, 303.15, 308.15)K and excess molar enthalpies, HE, for the same mixtures at temperature (298.15)K have been measured over entire range of mole fraction under atmospheric pressure. Using experimental data, excess molar volumes, VE, excess isentropic compressiblities, κSE, excess molar enthalpies, HE and excess molar heat capacities, CPE have been determined. The VE, κSE, HE and CPE data have been fitted to Redlich-Kister equation to estimate the binary adjustable parameters and standard deviations between experimental and calculated values. The topology of the constituent molecules (Graph theory) has been utilized to predict VE, κSE, HE and CPE data of the studied mixtures. The comparison of VE, κSE, HE and CPE values determined by Graph theory with their corresponding experimental values lends additional support to the proposed molecular entities existing in mixtures along with various processes involved in the (i+j) mixtures formation. Further, IR studies and quantum mechanical calculations support the presence of proposed molecular entities in the studied mixtures.