Enthalpies of mixing and excess Gibbs free energies of mixtures of octamethylcyclotetrasiloxane+cyclopentane at 291.15, 298.15, and 308.15 K

Abstract

The enthalpies of mixing of octamethylcyclotetrasiloxane+cyclopentane have been measured at 291.15, 298.15, and 308.15 K with an isothermal displacement calorimeter. Vapour pressures of the mixtures have been measured at the same temperatures by a precision static vapour pressure method. The enthalpy of mixing has a maximum of 227 J mol −1 at 291.15 K and the enthalpies decrease with increase in temperature. The excess Gibbs free energy, calculated from the vapour pressures, has a minimum of −199 J mol −1 at 291.15 K. This function becomes more negative with increase in temperature. The excess volumes, measured previously, change sign with composition and are independent of temperature.