Isotherms of Peng-Robinson Equation of State

Equations of state, determined empirically or theoretically, can determine the thermodynamic properties of fluids. Equations of state correlate the temperature, pressure, and volume of fluids.
Because of its simplicity, the Peng–Robinson equation of state (a cubic equation) is extensively used to predict the behavior of several fluids with reasonable accuracy. Its input parameters are the critical temperature, critical pressure, and accentric factor.
A common way to represent equations of state is to plot isotherms in the - plane. This Demonstration plots isotherms of a generic fluid, showing the influence of the parameters on the shape of the curves.
The critical isotherm is shown as a reference. Cubic equations have distinct characteristics for temperatures above and below the critical point.
Cubic equations can produce metastable regions and non-physical regions (negative pressures, for example).


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


Snapshot 1: temperatures below critical value
Snapshot 2: temperatures above critical value
Snapshot 3: combination of parameters that produce non-physical negative pressures
[1] J. R. Elliot and C. T. Lira, Introductory Chemical Engineering Thermodynamics, Upper Saddle River, NJ: Prentice Hall, 1999.
    • 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+