Immiscible Liquids Phase Diagrams: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • If a pure liquid is present, it exerts its own saturation pressure, independent of other pure liquid phases present.
  • For immiscible liquids, the partial pressure of a component in the vapor phase is always less than or equal to its saturation pressure.
  • When a vapor mixture (for components that are immiscible in the liquid phase) cools or its pressure increases, one component condenses first unless the vapor mole fractions are proportional to their saturation pressures.
  • For a given temperature, two immiscible liquids are in equilibrium with the vapor phase at only one pressure.
  • For a given pressure, two immiscible liquids are in equilibrium with the vapor phase at only one temperature.
From studying this module, you should now be able to:
  • Construct a pressure-composition diagram at a given temperature for two immiscible liquids, given saturation pressures at that temperature.
  • Construct a temperature-composition diagram at a given pressure for two immiscible liquids, given Antoine equations (saturation pressure versus temperature) for each component.
  • Determine what phases are present, given temperature, pressure, saturation pressures, and overall compositions.
  • Given a vapor composition and saturation pressure data, determine the temperature (at constant pressure) or the pressure (at constant temperature) at which one or more components condenses.


Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder