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 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.