Raoult's Law and Vapor-Liquid Equilibrium: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Raoult’s law assumes ideal gases and ideal liquid solution. For similar molecules (e.g., n-hexane and n-octane), Raoult’s law may be a good approximation.
  • When a vapor mixture is cooled or its pressure is increased, both components condense.
  • Bubble pressure is the pressure where the first bubble of vapor forms as the pressure above a liquid decreases at constant temperature.
  • Bubble temperature is the temperature where the first bubble of vapor forms as the temperature of a liquid increases at constant pressure.
  • Dew pressure is the pressure where the first drop of liquid forms as the pressure of a vapor increases at constant temperature.
  • Dew temperature is the temperature where the first drop of liquid forms as the temperature of a vapor decreases at constant pressure.
  • Unlike a pure component, at constant pressure a mixture does not evaporate at constant temperature.
From studying this module, you should now be able to:
  • Given a vapor composition and saturation pressure versus temperature data, determine the dew temperature (at constant pressure) or the dew pressure (at constant temperature).
  • Given a liquid composition and saturation pressure versus temperature data, determine the bubble temperature (at constant pressure) or the bubble
    pressure (at constant temperature).
  • Use Raoult’s law to calculate equilibrium compositions and/or equilibrium pressures for ideal solutions and ideal gases.
  • Construct a pressure-composition diagram for an ideal mixture given saturation pressures at a given temperature.
  • Construct a temperature-composition diagram for an idea mixture given Antoine equations at a given pressure.
 

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