Enthalpies of Mixing for Binary Liquid Mixtures of Monocarbonic Acids and Alcohols

We present the results of calorimetric measurements of the molar enthalpy of mixing (molar excess enthalpy) H̄E as a function of temperature and composition (described by the mole fraction x of the alcohol) for 18 binary liquid systems consisting of an aliphatic monocarbonic acid (formic, acetic, propionic, butyric, valeric acids) and an aliphatic alcohol (methanol, ethanol, 1-propanol. 2-propanol, 1-butanol, 2-methyl-2-propanol). The experiments cover temperatures between 298.15 K and 318.15 K and the whole range of compositions (usually nearly 40 compositions at each temperature). There is a great variety of behaviour as far as the function H̄E(x) for T= const is concerned. Many systems show endothermic mixing ( H̄E > 0), other systems exothermic mixing (H̄E < 0), again other systems partly endothermic, partly exothermic behaviour. There is one case (acetic acid + 2-methyl-2-propanol) where H̄E(x) changes its sign twice and the molar excess heat capacity exhibits unusually large negative values.