Špela Paljk

Partial molar volumes and partial molar expansibilities of cholesterol in some aprotic solvents

Abstract The densities of solutions of cholesterol (up to 0.4 mol kg −1 ) in benzene, toluene, carbon tetrachloride, chloroform or 1,2-dichloroethane were measured at 293, 298, 303, 313, 323 and 333 K. The partial molar volumes and partial molar expansibilities of the solute were found to be independent of concentration. The thermal expansion coefficients of the solute in the studied solvents tended to decrease slightly with increasing temperature. The thermal expansion coefficients of the investigated solutions decreased with increasing concentration. In addition, the partial molar volumes of the solute at infinite dilution are discussed on the basis of scaled particle theory. The “solvent effect” on the partial molar volume of the solute was found to be due mainly to cavity formation and intermolecular dispersion forces.

Solubility of tetracosane in aliphatic alcohols

Abstract Solubilities of tetracosane (C 24 ) in aliphatic alcohols (1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, l-nonanol, 1-decanol, 1-undecanol, 1-dodecanol) have been determined at temperatures ranging from the melting point of the solute to 289 K. Five methods of correlation have been applied: Wilson, simple UNIQUAC, UNIQUAC associated-solution model as well as two modified NRTL equations. The root mean square deviations of the solubility temperatures for all measured data vary from 0.11 K to 2.43 K and depend on the particular equation used. The best solubility correlation has been obtained with the UNIQUAC associated-solution model. In the calculations, the existence of a solid-solid first-order phase transition in tetracosane has also been taken into consideration.

Thermodynamic functions of activation for viscous flow of cholesterol in some non-aqueous solutions

Abstract The viscosities of solutions of cholesterol in benzene, toluene, carbon tetrachloride, chloroform and 1,2-dichloroethane up to 0.4 mol kg −1 at 293, 298, 303, 313, 323 and 333 K have been measured. On the basis of Eyrings theory of rate processes, the molar thermodynamic functions of activation for viscous flow of solution, i.e. the molar Gibbs free energy Δ# Ḡ 1,2 , molar enthalpy, Δ# H H 1,2 and molar entropy, Δ# S 1,2 , and corresponding partial molar quantities of activation for viscous flow of solute and solvent have been determined. Additionally, the viscosity coefficients B and D and their temperature derivatives are calculated and correlated with solvent dielectric parameter β. The influence of the “solvent effect” on the above parameters is discussed on the basis of Eyrings theory of the transition state and the structure of solution.

Excess enthalpies of nonan-1-ol and undecan-1-ol with octane at high dilutions and at 298.15 K

Abstract Heats of mixing at high dilutions were determined for binary systems consisting of nonan-1-ol or undecan-1-ol and n -octane at 298.15 K. Partial molar heats of mixing at infinite dilution, giving approximate values of hydrogen bonding energies in alcohols, were determined by extrapolation of the experimental data to zero concentrations of the alcohols ( x 1 = 0). The results are correlated by means of polynomials, the UNIQUAC and the UNIQUAC associated-solution models. The ability of these equations to represent the thermodynamic functions of dilute mixtures of alkan-1-ols in n -alkanes at 298.15 K is discussed.

Thermodynamic functions of activation for viscous flow of some monosaccharides in aqueous solutions

Abstract The viscosities of aqueous solutions of some monosaccharides D-pentoses and (D-hexoses) were measured up to 2.5 mol kg −1 in the temperature range from 293.15 to 318.15 K. On the basis of Eyrings theory of the transition state, the relations for the thermodynamic functions of activation for viscous flow of binary liquid mixtures, i.e. molar Gibbs free energy, Δ # Ḡ 1,2 , entropy, Δ # S 1,2 , and enthalpy, Δ # H 1,2 , and for the partial molar quantities of activation for viscous flow of solute and solvent, respectively, were obtained. Thereby, the dependence of the molar thermodynamic functions of activation for a viscous flow of solution against the solute mole fraction was given as a second-degree polynomial. It was shown that the linear correlation coefficient β Y , ( Y denotes G , H or S ), is given by the difference between the partial molar activation parameter of the solute at infinite dilution and the respective molar quantity of the pure solvent. In addition, correlations between the coefficient β Y and the viscosity coefficient B and/or temperature derivative of the viscosity coefficient B were found. For the solutions investigated, the molar thermodynamic activation parameters for viscous flow were found to be linearly dependent on the solute mole fraction, which means that the partial molar quantities of activation of the solutes are concentration independent.

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

Abstract 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.

Hydration of tri-n-hexyl amine hydrochloride, tri-n-octyl amine hydrochloride, tri-n-decyl amine hydrochloride and tri-n-dodecyl amine hydrochloride benzene solutions

Abstract Isopiestic equilibrations of THxA·HCl, TOA·HCl, TDA·HCl and TLA·HCl benzene solutions have been made in the concentration range from 0·02 to 0·13 mole/kg at different water activities and 25°C. The mean hydration number of the chloride ion at unit water activity was found to be 1·024±0·015 for the systems investigated. To determine the effect of water activity on the amine salt activity the results were treated on the basis of the Gibbs-Duhem equation and a simple linear relation obtained between salt and water activities. IR spectrophotometric measurements were performed to identify the nature of the hydrated species.

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

Abstract 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 Bjerrums 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.

Thermodynamics of aggregation of tri-n-octylammonium halides in benzene solutions

The freezing temperatures of dilute benzene solutions of tri-n-octylammonium halides were measured over the concentration range 0.01–0.3 mol kg–1. The relative apparent molar enthalpies of these systems up to 0.55 mol kg–1 were determined calorimetrically at 298.15 K. The practical osmotic coefficients and molal activity coefficients were calculated at the freezing point of benzene, i.e. 278.68 K, while the excess thermodynamic functions were calculated at 298.15 K. The non-ideal behaviour of the systems investigated was described on the basis of an association model, in which the first stepwise association reactions occur less readily than the rest. Thereby, the association equilibria were treated by two independent parameters: the dimerization constant β2 and constant K, both of which were obtained from the experimental data by a curve-fitting method.

Partial molar volumes, partial molar expansibilities and viscosity of benzene solutions of tri-n-octylammonium halides

The densities of benzene solutions of tri-n-octylammonium chloride, tri-n-octylammonium bromide and tri-n-octylammonium iodide up to 0.25 mol kg–1 at 293.15, 298.15, 303.15, 313.15 and 323.15 K were measured. The partial molar volumes and partial molar expansibilities of the solutes were found to be independent of concentration, and the partial molar expansibilities were found to be equal for all the solutes investigated. For these systems viscosity measurements were also made and the viscosity coefficients B and D determined. In addition, the relative viscosity was interpreted on the basis of the theory of rate processes and regular solution theory, and thermodynamic functions of activation for viscous flow and the solubility parameters of the solutes investigated were calculated at 298.15 K.