# PengRobinson EOS in FPROPS

*This article is about*

**planned development**or**proposed**functionality. Comments welcome.Work on this is went on as a part of GSoC 2010 (Project Ankit) and continues as part of GSoC 2011 (Richard Towers). See also FPROPS.

Comments and suggestions are welcome

## Overview

The Peng-Robinson EOS is a cubic equation of state in that it contains volume terms to the third power. It is usually expressed to give pressure in terms of temperature and molar volume :

where

It is sometimes more convenient to express the equation as a cubic polynomial in terms of compressibility factor

in which

## Departure Functions

Departure functions represent the departure of the *real* properties from the *ideal* properties - i.e the properties of a fluid at zero pressure or infinite molar volume.
The departure functions of the Peng-Robinson equation of state are as follows:

Clearly to evaluate these functions we need to be able to evaluate (checked, agrees with Sandler):