Using a Cubic EOS to Determine Vapor-Liquid Equilibrium: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • An equation of state (EOS) can be used to model non-ideal behavior in both vapor and liquid phases.
  • The fugacity coefficient for a given component is its fugacity divided by its partial pressure.
  • Compositions of liquid and vapor phases in equilibrium can be determined from an EOS for non-ideal mixtures.
  • In general, when liquid and vapor phases are in equilibrium for mixtures, the compositions will be different in the two phases.
  • This module uses the Peng-Robinson EOS to determine VLE, but the approach is identical for other EOSs.
From studying this module, you should now be able to:
  • Apply mixing rules to determine parameters to use in a cubic EOS.
  • Apply a cubic equation of state (EOS) to determine bubble and dew points for multi-component mixtures.


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