The Thermal Pressure and Energy–Volume Coefficients of the Methyl Alcohol – Water and <i>t</i>-Butyl Alcohol – Water Systems

Thermal pressure and energy–volume coefficients have been determined for various methyl alcohol – water and t-butyl alcohol – water mixtures at several temperatures in the range 19–55 °C. The energy–volume coefficient is found to pass through a maximum at 0.3–0.4 mole fraction methyl alcohol and 0.1 mole fraction t-butyl alcohol. This behavior is consistent with the average intermolecular distance passing through a minimum in both systems at the corresponding solvent compositions. The relationship between the energy–volume coefficient, the cohesive energy density, and the structure of aqueous binary systems is examined. The temperature dependence of the thermal pressure coefficient is discussed in terms of the effect of temperature on the susceptibility of the entropy of the two systems to isothermal expansion.