Thermodynamics of hydrogen-bonding mixtures 2.G E,H E,andS E of 1-propanol +n-heptane

A metal ebulliometcr was used to measure total vapor-pressure (PTx) data on 18 mixtures of 1-propanol +n-heptane (and the pure components) between 380 and 445 K. Bubble-point data were measured at seven pressures between 200 kPa and I MPa. These data cover an intermediate region between previous data reported near atmospheric pressure and below and high-temperature data extending to the critical region. A Redlich--Kister G' model fit isotherms between 373.15 and 463.15 K via Barker's method with an average standard error of 0.2 to 0.5% in pressure. The system exhibits large positive deviations from ideality (derived =2.7–10.5) which decrease with temperature. EquimolarG ^E/T values thus derived also decrease with increasing temperature, which predicts a positiveH ^E An azeotrope exists under all conditions studied: the azeotropic composition increases in alcohol content with increasing temperature. These mixture thermodynamic data show that, above 345 K, the system 1-propanol +n-heptane belongs to the class of mixtures whereG ^E > 0,H ^E >0. andTS ^E > 0. This probably occurs because the 1-I orientational effect (in this case, hydrogen-bonding of the alcohol molecules) is more readily disrupted in the inert solvent than it would be a( lower temperatures, where the effect of hydrogen-bonding is stronger.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.