- Acentric factor
In
thermodynamics , the acentric factor is a factor originally used by K.S. Pitzer and coworkers as an expression in an equation for thecompressibility factor . It is defined as.
stands for the
reduced temperature .For most simple fluids at is close to 0.1, therefore . In many cases, lies near the
normal boiling point .Acentric factor accounts for characteristic of molecular structure. Values of can be determined for any fluid from , and a single-vapor measurement made at = 0.7. Values of are tabulated in many thermodynamic tables.
The definition of makes its value zero for argon, krypton, and xenon, and experimental data yield compressibility factors for all three fluids that are correlated by the same curves when Z (compressibility factor) is represented as a function of Tr and Pr. This is the basic premise of the following three-parameter theorem of corresponding states:::All fluids having the same value of , when compared at the same Tr and Pr, have about the same value of Z, and all deviate from idea-gas behavior to about the same degree.
ee also
Equation of state
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