Excess molar enthalpies of (an alkanoic acid plus n-heptane, or cyclohexane, or benzene) at T=298.15 K

A flow microcalorimeter of the Picker design was used to measure excess molar enthalpies HE at the temperature 298.15 K over the whole composition range of several binary liquid mixtures formed from an alkanoic acid and either n-heptane, or cyclohexane, or benzene. The alkanoic acids selected were ethanoic acid (acetic acid), propanoic acid (propionic acid), butanoic acid (butyric acid), hexanoic acid (caproic acid), and octanoic acid (caprylic acid). The excess molar enthalpies are all of more or less parabolic shape with the H-m(E) values at mole fraction x = 0.5 and T = 298.15 K decreasing in the series with n-heptane from 590 J. mol(-1) for {xC(2)H(5)COOH + (1 - x)n-C7H16} to 235 J. mol(-1) for (xC(7)H(15)COOH + (1 - x)n-C7H16}; in the series with cyclohexane, the corresponding values are 698 J. mol(-1) and 464 J. mol(-1), respectively. In the series with benzene as the second component, however, the H-m(E), values at x = 0.5 first decrease from 288 J. mol(-1) for (xCH(3)COOH + (1 - x)C6H6 to 110 J. mol(-1) for {xC(2)H(5)COOH + (1 - x)C6H6), and then increase slowly for the mixtures with the higher acids. (C) 1999 Academic Press.