THERMODYNAMICS OF LIQUID-MIXTURES CONTAINING - N-ALKANES AND STRONGLY POLAR COMPONENTS - VE AND CPE OF MIXTURES WITH EITHER PYRIDINE OR PIPERIDINE

Excess molar volumes V(E) and excess molar heat capacities C(P)E at constant pressure have been obtained, as a function of mole fraction x1, for several binary liquid mixtures belonging either to series I: pyridine + n-alkane (C1H21+2), with l = 7, 10, 14, 16, or series II: piperidine + n-alkane, with l = 7, 8, 10, 12, 14. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. V(E) of pyridine + n-heptane shows a S-shaped composition dependence with a small negative part in the region rich in pyridine (x1 > 0.90). All the other systems show positive V(E) only. The excess volumes increase with increasing chain length l of the n-alkane. The excess molar heat capacities of the mixtures belonging to series II are all negative, except for a small positive part for piperidine + n-heptane in the region rich in piperidine (x1 > 0.87). The C(P)E at the respective minima, C(P)E(x1,min), become more negative with increasing l, and the x1,min values range from about 0.26 (l = 7) to 0.39 (l = 14). Most interestingly, mixtures of series I exhibit curves of C(P)E against x1 with two minima and one maximum, the so-called W-shape curves.