This is a cubic EOS developed especially for light natural gas components. It constituted a major improvement over the van der Waals EOS. Later it was superseded by the Redlich–Kwong–Soave EOS, but for very high temperatures the original Redlich–Kwong equation may still be better.

The equation gives decent vapour pressure curves for small nonpolar compounds; molar volumes and caloric data are usually not represented well.

The critical compression factor of this EOS is fixed. It is not possible for this EOS to match all 3 critical conditions.

adjustable parameters: 2

For mixture calculations the following mixing theories are available:

[1] O. Redlich and J.N.S. Kwong, Chem. Reviews 44 (1949) 233–244.

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