General two-parameter equation of state

The generalized two-parameter cubic equation of state takes the form:

where:

P is pressure

R is the ideal gas constant

T is absolute temperature

V is molar volume

a is at the critical temperature ac, is the first derivative of pressure with volume set to zero

b is at the critical temperature bc, is the second derivative of pressure with volume set to zero

u and w are constants (typically integers)

Different values for the constants u and w give different specialized equations of state, such as the van der Waals equation, the Peng-Robinson equation, and the Redlich-Kwong equation. See PR — Peng-Robinson equation of state and RK — Redlich-Kwong equation of state for more information.