Redlich-Kwong equation of state
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The Redlich-Kwong equation of state is an equation of state for real gases that was found in 1949 by Otto Redlich and Joseph Neng Shun Kwong . It improves the Van der Waals equation only marginally, but is still of interest today due to its comparatively simple form.
Further developments are the Soave-Redlich-Kwong equation of state and the PSRK equation of state .
formulation
The Redlich-Kwong equation of state reads:
With
- Cohesive pressure
- Co-volume
- - molar volume
- - temperature
- - critical temperature
- - pressure
- - critical pressure
- - universal gas constant .
With the reduced state variables , the equation of state can be written in the reduced form :
with .
scope of application
The Redlich-Kwong equation is suitable for the calculation in gas phases if the ratio of pressure to critical pressure is less than half the ratio of temperature to critical temperature .:
Equivalent: the reduced pressure may be a maximum of half the size of the reduced temperature :
A poor approximation is shown for liquid phases, which is why the equation cannot be used for gas-liquid equilibria . However, this disadvantage can be compensated for by using better fitted equations separately.
literature
- Otto Redlich , JNS Kwong: On the Thermodynamics of Solutions. V. An Equation of State. Fugacities of Gaseous Solutions. In: Chemical Reviews . tape 44 , no. 1 , 1949, p. 233-244 , doi : 10.1021 / cr60137a013 .