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The Redlich–Kwong equation is very similar to the Van der Waals equation, with only a slight modification being made to the attractive term, giving that term a temperature dependence. At high pressures, the volume of all gases approaches some finite volume, largely independent of temperature, that is related to the size of the gas molecules.
In 1972 G. Soave [4] replaced the term of the Redlich–Kwong equation with a function α(T,ω) involving the temperature and the acentric factor (the resulting equation is also known as the Soave–Redlich–Kwong equation of state; SRK EOS).
Hence, all cubic equations of state can be considered 'modified van der Waals equation of state'. There is a very large number of such cubic equations of state. For process engineering, cubic equations of state are today still highly relevant, e.g. the Peng Robinson equation of state or the Soave Redlich Kwong equation of state.
Critical isotherm for Redlich-Kwong model in comparison to van-der-Waals model and ideal gas (with V 0 =RT c /p c) The Redlich–Kwong equation is another two-parameter equation that is used to model real gases. It is almost always more accurate than the van der Waals equation, and often more accurate than some equations with more than two ...
The most famous functional forms of this category are Redlich-Kwong, [3] Soave-Redlich-Kwong [4] and Peng-Robinson. [5] Although their initial form is empirically suggested, they are categorised as semi-empirical models as their parameters can be adjusted to fit the real experimental measurement data of the target system.
PSRK is a group-contribution equation of state. This is a class of prediction methods that combines equations of state (mostly cubic) with activity coefficient models based on group contributions, such as UNIFAC. The activity coefficient model is used to adapt the equation-of-state parameters for mixtures by a so-called mixing rule.
VTPR is a group contribution equation of state. [3] This is class of prediction methods combine equations of state (mostly cubic) with activity coefficient models based on group contributions like UNIFAC. [4] The activity coefficient model is used to adapt the equation of state parameters for mixtures by a so-called mixing rule. [5]
Otto Redlich (November 4, 1896 – August 14, 1978) was an Austrian physical chemist who is best known for his development of equations of state like the Redlich-Kwong equation. [ 1 ] [ 2 ] Redlich also made numerous other contributions to science.