EXCESS PARTIAL MOLAR FREE-ENERGIES AND ENTROPIES IN AQUEOUS TERT-BUTYL ALCOHOL-SOLUTIONS AT 25-DEGREES-C

The total vapor pressures of tert-butyl alcohol (TBA)-water mixtures were measured at closely spaced mole fractions. The excess partial molar free energies for 25.00°C, GmE(i) (i = TBA or H2O) were calculated by the Boissonnas method. In the range where the Boissonnas method is not appropriate, the Guggenheim expression for the excess integral molar free energy, GmE, was used to analyze the data. The excess partial molar enthalpies, HmE(i) (i = TBA or H2O), at 25.00°C were calculated from the data of the previous calorimetric works from this laboratory. The excess partial molar entropies, SmE(i) (i = TBA or H2O), were then calculated. These data show that there are changes in the mixing scheme, or the "structure" of these solutions, at about xB = 0.045 and xB = 0.62. (xB is the mole fraction of TBA in the liquid phase.) The first crossover is associated with an anomaly in the quantities that are proportional to the third derivative of the free energy, while the second is accompanied by an anomaly in the fourth derivative. We suggest that the first crossover is the transition of a short to intermediate range order, while the latter is a transition of more subtle nature. © 1990 American Chemical Society.