Relative Molar Enthalpy Research Articles

An enthalpic approach to delineate the interactions of cations of imidazolium-based ionic liquids with molecular solvents

We present a systematic investigation on the enthalpic assessment of the interactions operating between the cation and anion of four imidazolium ionic liquids with aqueous and various nonaqueous solvents. Accurate experimental information gathered with the help of an isothermal titration calorimeter at 298.15 K has been analyzed for excess partial molar enthalpy of the ionic liquid, H(IL)(E), in terms of hydrophobic and solvation effects. The variations in the limiting excess partial molar enthalpy of the ionic liquid, H(IL)(E, ∞), have been correlated with solvent properties. We have quantified the enthalpic effects due to dissociation of ionic liquids in very dilute solutions and to clathrate formation with the increasing concentration of ionic liquid. A change in enthalpic behavior from endothermic to exothermic is observed on increasing the carbon chain length attached to the imidazolium ring. The solvent reorganization around the cationic species has been unraveled by employing the ionic liquid interaction parameters called as H(IL-IL)(E) deduced from the H(IL)(E) data. The apparent relative molar enthalpy, φ(L), derived from H(IL)(E) data has been examined in the light of the specific ion interaction theory as advanced by Pitzer with accurate results.

Enthalpy of Dilution of Aqueous [C4mim][Gly] at 298.15 K

A novel amino acid ionic liquid [C4mim][Gly] (1-butyl-3-methylimidazolium glycine) was prepared by a neutralization method. The molar enthalpies of dilution, ΔDHm(mi→mf), of aqueous [C4mim][Gly] at various molalities were measured at (298.15 ± 0.01) K. The values of the apparent relative molar enthalpy, φL, were calculated by using both the extended Debye−Huckel equation and the Pitzer equation, which were in good agreement within experimental error. In terms of φL, the molar enthalpies of solution of [C4mim][Gly], ΔsHm, at various molalities were estimated. The estimated values of ΔsHm were consistent with the experimental values previously obtained.

Thermochemistry on ephedrine hydrochloride and N-methylephedrine hydrochloride

The crystal structures of ephedrine hydrochloride and N-methylephedrine hydrochloride have been determined by X-ray crystallography. The molar enthalpies of dissolution of the two compounds with various molalities were measured at T = 298.15 K in distilled water by means of isoperibol solution-reaction calorimeter, respectively. According to the theory of Pitzer, the molar enthalpies of dissolution of the two compounds at infinite dilution, Δ s H m ∞ , and Pitzer’s parameters β MX ( 0 ) L , β MX ( 1 ) L , and C MX Φ L , were obtained. Then the values of apparent relative molar enthalpies ( Φ L ) , hydration heat, and relative partial molar enthalpies of the two compounds ( L ¯ 2 ) were derived from the experimental results of the enthalpies of dissolution of the two compounds. Finally, the ionic radius of the cations can be calculated from the data of the corresponding effective volume of the cations.

Description of dilution enthalpies and heat capacities for aqueous solutions within the MSA–NRTL model with ion solvation

The capability of the MSA–NRTL model to describe heat effects for binary aqueous electrolyte and nonelectrolyte solutions, with a relatively reduced number of parameters, is examined. The thermodynamic properties described include the osmotic coefficient, ϕ , the apparent relative molar enthalpy, Φ L , and the apparent molar heat capacity, Φ C P . The MSA–NRTL model consists of the mean spherical approximation (MSA) for the long-range electrostatic contribution to the Gibbs energy (for ionic solutions) and a local composition model, the non-random two-liquid (NRTL) model for the short-range contribution.

A Thermodynamic Approach to a Density Model for Oxide Melts

In an attempt to estimate the densities of complex slags, a model based on the thermodynamics of slags developed earlier by the present authors is extended to ternary and multi‐component systems in the present work. The molar volumes of ternary and higher order systems were derived from the relative integral molar enthalpies of mixing of the corresponding slags. The higher order of slag systems has been predicted by using the parameters from the related binary sub‐systems, which have been evaluated earlier. Comparisons of calculated results with experimental data on molar volumes available in literature show a satisfying agreement for a number of systems, within the limits of experimental uncertainties. The model presents a promising method to compute the molar volume of slag systems where no experimental data is available using the abundance of thermodynamic data available. The model would also enable the generation of density data for slags containing Al2O3, CaO, FeO, MgO, MnO, and SiO2 compatible with the corresponding thermodynamic data.

Studies on enthalpy of solution for ionic liquid: The system of 1-methyl-3-ethylimidazolium tetrafluoroborate (EMIBF 4)

The molar solution enthalpies of ionic liquids (IL) EMIBF 4 (1-methyl-3-ethylimidazolium tetrafluoroborate), EMIC (1-methyl-3-ethylimidazo-lium chloride) and ionic solid NaBF 4 at various molalities were determined by the solution-reaction isoperibol calorimeter in water at 298.15 K. In terms of a Debye–Hückel limiting term, the molar solution enthalpies of EMIBF 4, EMIC and NaBF 4 at infinite dilution, Δ s H m ° , were obtained. Then the values of apparent relative molar enthalpy were calculated. Hydration heat of both cation EMI + and anion BF 4 − was discussed. In terms of values of Δ s H m ° , the reaction heat of NaBF 4 + EMIC → EMIBF 4 + NaCl was estimated.

Studies of Thermochemical Properties of a New Ionic Liquid Prepared by Mixing 1-Methyl- 3-Pentylimidazolium Chloride with InCl3

A new ionic liquid, PMIInCl4, was prepared by mixing 1-methyl-3-pentylimidazolium chloride (PMIC) with InCl3. The molar enthalpies of solution of PMIC and PMIInCl4 in water to form solutions at various molalities were determined at 298.15 K using an isoperibol calorimeter. Using Pitzer's electrolyte solution model, the molar enthalpies of solution of PMIC and PMIInCl4 at infinite dilution, Δsol H^m, and Pitzer's ion-interaction parameters βMX(0)L, βMX(1)L and CMXϕL, were derived. The values of the apparent relative molar enthalpy L and relative partial molar enthalpy of the solutes (PMIC and PMIInCl4), \(\bar{L}_{2}\), were subsequently calculated. Using the values of Δsol H^m of PMIC, PMIInCl4 and InCl3, the enthalpy change, Δr<H=−38.19kJ·;mol-1, was calculated for the reaction PMIC + InCl3 → PMIInCl4

Thermo-chemical properties of aqueous solution containing ionic liquids: 1. The heat of reaction mixed 1-methyl-3-butylimidazolium chloride with InCl 3

The ionic liquid BMIInCl 4 was prepared by mixing 1-methyl-3-butylimidazolium chloride (BMIC) with InCl 3. The molar solution enthalpies of BMIC and BMIInCl 4 at various molalities were determined by the solution reaction isoperibol calorimeter in water at 298.15 K. In terms of Pitzer's electrolyte solution theory, the molar solution enthalpy of BMIC and BMIInCl 4 at infinite dilution, Δ s H m ° and the parameters: β MX ( 0 ) L , β MX ( 1 ) L and C MX ϕ L were obtained. Then the values of apparent relative molar enthalpy ϕ L and relative partial molar enthalpies of solute (BMIC and BMIInCl 4), L 2, were calculated, respectively. In terms of values of Δ s H m ° of BMIC, BMIInCl 4 and InCl 3, the enthalpy change for the reaction: BMIC + InCl 3 → BMIInCl 4 was obtained.

Dissolution enthalpy of anhydrous sodium sulfate in water. Experimental measurements and treatment with the electrolyte-NRTL model

Dissolution enthalpies of anhydrous sodium sulfate in water were measured up to saturation atT= (287.8, 317.5, and 352.1) K with a SETARAM C80 mixing calorimeter. Experimental isotherms, and previous ones at T= 297.6 K and T= 317.5 K (Hubert, N. et al., Thermochim. Acta1995, 259, 41–48), all intersect around a molality of 2 mol · kg−1. These five isotherms have been fitted with the electrolyte-NRTL model according to a methodology presented in this paper. This methodology uses enthalpy values along with values atT= 298.15 K from the literature and leads to the proposal of a unique set of parameters that allows a simultaneous representation of dissolution enthalpies, apparent relative molar enthalpies, and osmotic coefficients of sodium sulfate in water. Very good agreement was obtained between experimental and calculated values of dissolution enthalpies and osmotic coefficients in (water + sodium sulfate).

Kinetics of hydrogen absorption and thermodynamics of dissolved hydrogen in Tb 1− xZr xFe 3 system

The kinetics of hydrogen absorption in the PuNi 3 type rhombohedral Tb 1− x Zr x Fe 3 ( x=0.1, 0.2, 0.3) system are studied in the temperature range 75≤ T(°C)≤150 at an initial pressure of 20 bar. By fitting the experimental kinetic data to a second order rate equation, the different phases [ α, ( α+ β), β] and phase boundaries [ α→( α+ β), ( α+ β)→ β] of the alloy-hydrogen system are identified. The thermodynamical parameters viz. the relative molar enthalpy (Δ H H) and the relative molar entropy (Δ S H) of dissolved hydrogen are evaluated using the vant Hoff equation and are found to be in the ranges −(8 to 28) kJ (mol H) −1 and −(32 to 66) J K −1 (mol H) −1 respectively. From the dependence of Δ H H with hydrogen concentration of the alloy-hydrides, the different phases [ α, ( α+ β), β] and phase boundaries [ α→( α+ β), ( α+ β)→ β] of the alloy-hydrogen system are identified. The different phases identified by both kinetic and thermodynamic studies confirm those seen in the hydrogen absorption isotherms of the respective alloy.

Thermodynamic and19F NMR studies of antimony trifluoride in water

Densities, specific heat capacities per unit volume and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for antimony trifluoride in water as functions of concentration. From the first three properties the apparent and partial molar volumes, heat capacities and relative enthalpies were derived. As well, pH measurements in water at 25°C and19F NMR spectra in water and methanol at 33°C were also carried out. All the thermodynamic properties together with the chemical shifts abruptly change in the very dilute concentration region (<0.1m) and, then, tend to a constant value. These trends have been rationalized through a simple model based on an equilibrium of dissociation of SbF3 into two ionic species. From the simulation of all the data it is derived that two concomitant equilibria are present in solution: the hydrolysis process of SbF3 which explains the pH values and the ionic dissociation of SbF3 which accounts for the19F NMR data.

Thermodynamic studies in the system SmH 2SmH 3

Equilibrium hydrogen dissociation pressures have been measured as functions of composition and temperature for the samarium-hydrogen system in the range 448 to 623 K. Relative partial molar enthalpies in the composition region of continuous solid solutions from n=2 to 2.5 atoms H/atom Sm have been evaluated from van't Hoff plots. The interaction energy between hydrogen atoms and octahedral interstices is negative (4 ∼ 8 kJ mole) indicating attractive interaction. The hydrogen pressures associated with the transition process from cubic to hexagonal samarium hydride have been determined and the relative molar enthalpy and entropy of formation of hydrogen-deficient hexagonal SmH 3 have been calculated from the temperature dependence of the equilibrium pressures in the two-phase region. Due to the extreme high-purity conditions, the hysteresis found in this work is 6.5 times less than found in the past. No similarities have been found between the structures of La and Ce trihydrides deviating from the cubic symmetry and the phases observed in the SmH system.

Heats of solution of 1-nonanol, 1-decanol and 1-undecanol in cyclohexane at 298.15 K and 308.15 K

The enthalpies of solution of 1-nonanol, 1-decanol and 1-undecanol in cyclohexane were measured at 298.15 K. and 308.15 K. The experimental values of enthalpy changes per mole of solution as a function of solute mole fraction are given in the form of a second-degree polynomial. The hydrogen bond enthalpies of 1-alkanol molecules in the systems studied were obtained from the enthalpy changes per mole of solute at infinite dilution. In addition, the values of the relative molar enthalpy of the pure solutes, the relative partial molar enthalpy of the solutes and solvent, and the relative apparent molar enthalpy of the solutes were determined at 298.15 K and 308.15 K. On the basis of a semi-ideal model of associated solution, the practical molal osmotic coefficients and the molal activity coefficient of the solutes were calculated from the thermochemical data. The non-ideal behaviour of these systems was described by the excess thermodynamic functions of solution, as well as by the partial excess thermodynamic functions of solutes and solvent. The enthalpic pair interaction coefficients were determined in the sense of the McMillan-Mayer theory. The non-ideality of the investigated systems was also described on the basis of an association model with an extended series of multimers, assuming that each addition of monomer to the progressively growing oligomeric species is more difficult.

Heats of solution of 1-nonanol and 1-undecanol in n-hexane, n-heptane, n-decane and n-hexadecane at 298.15 K

The heats of mixing of 1-nonanol or 1-undecanol in n-hexane, n-heptane, n-decane and n-hexadecane were measured at 298.15 K. The enthalpy changes per mole of solution were expressed as a second degree polynomial in X, the mole fraction of solute in the concentration range studied. From the enthalpy changes per mole of solute at infinite dilution, the hydrogen-bond enthalpy of 1-alkanol molecules in the solvents investigated was determined. From thermochemical data the relative molar enthalpies of the pure solutes, the relative partial molar enthalpies of the solute and the solvent and the relative apparent molar enthalpies of the solutes were deduced. Assuming that the enthalpies of the stepwise associations are equal for both solutes in the solvents investigated, the practical osmotic coefficients were calculated from the apparent molar enthalpy of the solutes and the enthalpy of a stepwise association reaction on the basis of a semi-ideal model of associated solutions proposed by Prigogine. The molal activity coefficients of the solutes were determined via Bjerrum's relation. The non-ideal behaviour of these systems was described by the excess thermodynamic functions, i.e. the excess Gibbs free energy, excess enthalpy and excess entropy, as well as with partial molar excess Gibbs free energy of solute and solvent. Furthermore, the non-ideality of the investigated systems was treated on the basis of an association model with an extended series of multimers, supposing that the first stepwise associations occur more readily than the rest. In addition, the pair virial coefficients of the solutes were determined from the excess enthalpies of solutions according to McMillan-Mayer theory.

Gas-chromatographic study of the thermodynamic properties of systems containing linear alkenes and alkynes

The selectivity of silicone phases OV-101, OV-17 and OV-225 with respect to the retention indices and thermodynamic functions of solution (relative molar enthalpies, entropies and free energies) of n-alkene and n-alkyne isomers and homologs was investigated and correlated with the molecular structure of the isomers.

The enthalpy of dilution of HCl(aq) to 648 K and 40 MPa thermodynamic properties

Enthalpies of dilution of HCl(aq) have been measured to 648 K and 40 MPa over the molality range of about 0.01 to 15.6 mol·kg −1. At temperatures above 523 K the experimental results approach infinite dilution with a slope greater than the limiting-law slope, a clear indication of ion association. An analysis of the enthalpies of dilution in combination with existing thermodynamic results has produced a comprehensive model for the thermodynamic properties of HCl(aq). Three versions of the ion-interaction model were used depending on the range of temperature or molality. The unmodified ion-interaction model of Pitzer was adequate through 523 K and 7 mol·kg −1. Addition of a fourth coefficient extended the molality range to 16 mol·kg −1 through 523 K, and for temperatures above 523 K the second coefficient was given additional dependence on molality (a non-zero β (2) parameter). By using the density of water as an independent variable each version of the ion-interaction model covers the entire range of pressure through 40 MPa and the number of adjustable parameters is minimized. A comparison of the thermodynamic properties of HCl(aq) with those of NaCl(aq) demonstrated that HCl(aq) is somewhat more associated than NaCl(aq) at high temperatures and the enthalpy of ionization makes a significant contribution to the observed apparent relative molar enthalpy of HCl(aq).

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The oxygen dissociation pressure of hypostoichiometric neptunium oxide was measured by the gas-equilibrium method in the 1470 to 1850 K range. The oxide was heated on a thermobalance in H2OH2 gas mixtures. The partial relative molar free energy, enthalpy and entropy as a function of the O/Np-ratio are reported.

Oxygen potential of hypostoichiometric neptunium oxide between 1470 and 1850 K

The oxygen dissociation pressure of hypostoichiometric neptunium oxide was measured by the gas-equilibrium method in the 1470 to 1850 K range. The oxide was heated on a thermobalance in H 2O H 2 gas mixtures. The partial relative molar free energy, enthalpy and entropy as a function of the O/Np-ratio are reported.

Effect of geometry on the thermodynamic properties of micellar systems: trialkylamine oxides in water

The apparent molar volumes, heat capacities, relative enthalpies, and isentropic compressibilities of symmetrical trialkylamine oxides and cyclohexyldimethylamine oxide were measured in water at 25 °C. The data were in most cases analyzed with a mass-action model which was previously developed (J. Phys. Chem. 87, 1397 (1983)) for micellar systems. Trimethylamine oxide shows no sign of micellization while the three next members of this homologous series and cyclohexyldimethylamine oxide form aggregates with relatively low aggregation numbers. The thermodynamic data were compared with those of assymmetrical amine oxides to investigate the effect of geometry on the micellar properties. The thermodynamic properties of the solutes in the pre-micellar region show a very good group additivity which is independent of geometry. On the other hand, with symmetrical isomers, the CMCs are much larger, the aggregation numbers smaller and the thermodynamic functions of micellization larger. These geometrical factors can be taken advantage of for thermal energy storage.

Enthalpies of dilution from 50 to 225�C of aqueous decyltrimethylammonium bromide

Enthalpies of dilution of aqueous decyltrimethylammonium bromide have been measured from 0.56 to about .005 mol-kg−1 and from 50 to 225°C near the saturation pressure of water using a flow calorimeter. The changes of the stoichiometric osmotic and activity coefficients with temperature, the excess apparent molar heat capacity, and the apparent and partial relative molar enthalpies have been calculated from the data.