Thermodynamics of liquid binary (alkanenitrile–alkane) mixtures. Part 2.—Experimental excess molar heat capacity at 298.15 K and structure in solution
Abstract
Excess molar heat capacities at constant pressure (CEp) have been determined at 298.15 K, as a function of mole fraction, for 17 binary liquid mixtures of propanenitrile, butanenitrile, pentanenitrile and hexanenitrile mixed individually with some of the following alkanes: hexane, heptane, octane, decane, dodecane and tetradecane. CEp is positive and extremely large for propanenitrile with hexane and heptane, increasing in magnitude with the alkane chain length, 6 and 8 J mol–1 K–1 equimolar composition, respectively, whereas for the systems with butanenitrile, pentanenitrile and hexanenitrile as the common component, CEp, varies from small positive values for the systems with lower alkanes to negative values for the systems with the larger alkanes. For some of these systems the curve CEp(x) presents a ‘W shape’, i.e. it exhibits two minima separated by a maximum, that is, two changes of sign of the curvature. The observed behaviour is discussed in terms of structure in the solutions due to non-randomness or local concentration fluctuations and randomness balance. In this way, the concentration–concentration correlation function, Scc, is calculated using a molecular groups contribution model for the excess Gibbs energy of the systems studied in order to correlate these effects.