Molar excess volumes, isentropic compressions, and isobaric heat capacities of methanol – isomeric butanol systems at 298.15 K

Molar excess volumes, molar excess isentropic compressions, and molar excess isobaric heat capacities for binary liquid mixtures of methanol with 2-methylpropanol, 2-butanol, and 2-methyl-2-propanol have been determined at 298.15 K. The concentration dependence and magnitude of these thermodynamic functions are quite different from those of the methanol – 1-butanol system, which had been previously determined. Molar excess volumes for two of the present systems are positive over the whole concentration range, except for the 2-methyl-2-propanol system. For the latter system they are negative in the butanol-rich range. Molar excess isentropic compressions of these systems show slightly different concentration dependence from that of the excess volumes, but the order in magnitude resembles that of the excess volumes. Molar excess isobaric heat capacities for all systems are negative and show simple concentration dependence. The minimum values of excess heat capacities are correlated with the magnitude of molar isobaric heat capacities of the pure isomeric butanols. The behavior of these excess functions is discussed with reference to the differences in numbers and strength of hydrogen bonding between the pure liquid and the solution.