# Residual Functions for the SRK and PR Equations of State

Residual Functions for the SRK and PR Equations of State

In the gas phase, deviation from ideal behavior is taken into account by introducing residual functions, of the form . As pressure approaches zero, the gas behaves like an ideal gas, so that .

M=M-M

R

ig

M=M-M→0

R

ig

This Demonstration plots the gas-phase residual properties for the gas propylene versus temperature (in Kelvin) using either the Soave–Redlich–Kwong (SRK) or the Peng–Robinson (PR) equation of state (EoS) [1, 2]. Use the slider to set the value of the pressure (in bar) and choose among three thermodynamic properties: (enthalpy in J/mol), (entropy in J/mol.K) or (Gibbs free energy in J/mol). At , we get an excellent agreement between the results of our calculations (red curve for the SRK EoS, blue for PR EoS) and their counterparts obtained with the Aspen Plus process simulator [3] (green squares).

P

H

S

G

P=10bar