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 mol ar enthalpies HE at the temperature 298.15 K over the whole composition ran ge of several binary liquid mixtures formed from an alkanoic acid and eithe r n-heptane, or cyclohexane, or benzene. The alkanoic acids selected were e thanoic acid (acetic acid), propanoic acid (propionic acid), butanoic acid (butyric acid), hexanoic acid (caproic acid), and octanoic acid (caprylic a cid). The excess molar enthalpies are all of more or less parabolic shape w ith 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 46 4 J. mol(-1), respectively. In the series with benzene as the second compon ent, 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.