P-x-y and T-x-y Diagrams for Vapor-Liquid Equilibrium (VLE)

The vapor-liquid equilibrium (VLE) behavior of an -hexane/-octane mixture is demonstrated in and diagrams. The blue line represents the liquid-phase boundary (bubble point) and the green line represents the vapor-phase boundary (dew point). Click and drag the black dot on either diagram and the bar chart shows the amounts of liquid (blue) and vapor (green) present; the system contains a total of 1 mol. The mole fractions of -hexane in each phase ( for liquid phase, for vapor phase) are also shown in the bar graph. Use sliders to vary the temperature for the diagram or the pressure for the diagram. This system is modeled by Raoult's law because an -hexane/-octane liquid phase is assumed ideal.


  • [Snapshot]
  • [Snapshot]
  • [Snapshot]


The saturation pressure of component is calculated using the Antoine equation:
where for -hexane and for -octane, is saturation pressure (bar), , , and are Antoine constants, and is temperature (°C).
Raoult's law is used to calculate the bubble-point and dew-point pressures using the factors:
where is the vapor mole fraction and , is the liquid mole fraction and , and is the total pressure (bar).
The bubble-point pressure is calculated using :
The dew-point pressure is calculated using :
A screencast video at [2] shows how to use this Demonstration.
[1] J. R. Elliott and C. T. Lira, Introductory Chemical Engineering Thermodynamics, New York: Prentice Hall, 2012 pp. 372–377.
[2] P-x-y and T-x-y Diagrams for Vapor-Liquid Equilibrium (VLE). www.colorado.edu/learncheme/thermodynamics/PxyTxyDiagramsVLE.html.
    • Share:

Embed Interactive Demonstration New!

Just copy and paste this snippet of JavaScript code into your website or blog to put the live Demonstration on your site. More details »

Files require Wolfram CDF Player or Mathematica.

Mathematica »
The #1 tool for creating Demonstrations
and anything technical.
Wolfram|Alpha »
Explore anything with the first
computational knowledge engine.
MathWorld »
The web's most extensive
mathematics resource.
Course Assistant Apps »
An app for every course—
right in the palm of your hand.
Wolfram Blog »
Read our views on math,
science, and technology.
Computable Document Format »
The format that makes Demonstrations
(and any information) easy to share and
interact with.
STEM Initiative »
Programs & resources for
educators, schools & students.
Computerbasedmath.org »
Join the initiative for modernizing
math education.
Step-by-Step Solutions »
Walk through homework problems one step at a time, with hints to help along the way.
Wolfram Problem Generator »
Unlimited random practice problems and answers with built-in step-by-step solutions. Practice online or make a printable study sheet.
Wolfram Language »
Knowledge-based programming for everyone.
Powered by Wolfram Mathematica © 2018 Wolfram Demonstrations Project & Contributors  |  Terms of Use  |  Privacy Policy  |  RSS Give us your feedback
Note: To run this Demonstration you need Mathematica 7+ or the free Mathematica Player 7EX
Download or upgrade to Mathematica Player 7EX
I already have Mathematica Player or Mathematica 7+