Any thermodynamic property,
, can be expressed as the sum of an ideal gas contribution and a residual non-ideal contribution:
, where
and
are the ideal gas and residual contributions, respectively. For a given equation of state, the residual contribution can then be expressed as a function of
,
, and compressibility factor
. In this Demonstration, the compressibility factor for a single gas chemical species (acetylene) is computed, from which the enthalpy (
in
) and entropy (
in
can be determined for given
and
. You can select from one of three cubic equations of state (Redlich–Kwong, Soave–Redlich–Kwong, or Peng–Robinson) as well as the temperature (in
) and the pressure (in
). The reference state is taken an ideal gas at
and
. This information is then used to obtain the molar volume (in
) as well as additional thermodynamics properties such as the Gibbs free energy (
in
), Helmholtz free energy (
in
), and internal energy (
in
). In addition,
is plotted versus reduced pressure
for a user-specified reduced temperature (
), where
and
are the critical pressure and temperature for acetylene. For an ideal gas
.
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