Interactive Self-Study Module: Raoult's Law and Vapor-Liquid Equilibrium


This module uses screencasts and interactive simulations to explain the vapor-liquid phase equilibrium of two liquids that form an ideal solution. Both pressure-composition and temperature-composition diagrams are explained. It then provides step-by-step quiz simulations and example problems to allow the user to test themselves. Your retention of material in this module will increase if you write down reasons for your answers to ConcepTests, questions in screencasts, and questions to answer before using interactive simulations, and you try to solve the example problems before watching the screencast solutions. We suggest using the learning resources in the following order:

  1. Attempt to answer the multiple choice ConcepTest and solve the example problem before watching the screencasts or working with the simulations.
  2. Watch the screencast that describes the phase diagrams and answer the questions within the screencast.
  3. Review important equations for Raoult’s law and vapor-liquid equilibrium.
  4. Use the interactive simulations to further understand the behavior of the phase diagrams.
  5. Use the quiz interactive simulation(s) to test your understanding by carrying out step-by-step preparation of phase diagrams.
  6. Try to solve the example problems before watching the solutions in the screencasts.
  7. Answer the ConcepTests.
  8. Look at the list of key points, but only after you try to list the key points yourself. 
  • The differences in compositions of liquid and vapor mixtures in equilibrium is the basis for the separation of mixtures by distillation. 
  • This module is intended for material and energy balances, thermodynamics, and separations courses.
Before studying this module, you should be able to:
After studying this module, you should 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.