The acentric factor is a conceptual number introduced by Kenneth Pitzer in 1955, proven to be very useful in the description of matter. It has become a standard for the phase characterization of single & pure components. The other state description parameters are molecular weight, critical temperature, critical pressure, and critical volume (or critical compressibility).The acentric factor is said to be a measure of the non-sphericity (centricity) of molecules. As it increases, the vapor curve is "pulled" down, resulting in higher boiling points.
It is defined as:
For many monatomic fluids
is close to 0.1, therefore . In many cases, lies above the boiling temperature of gases at atmosphere pressure.
Values of can be determined for any fluid from , and a vapor measurement from , and for many liquid state matter is tabulated into many thermodynamical tables.
The definition of gives zero-value for the noble gases argon, krypton, and xenon. is almost exactly zero for other spherical molecules. Experimental data yields compressibility factors for all fluids that are correlated by the same curves when (compressibility factor) is represented as a function of and . This is the basis premises of three-parameter theorem of corresponding states:
Values of some common gases
- Adewumi, Michael. "Acentric Factor and Corresponding States". Pennsylvania State University. Retrieved 2013-11-06.
- Saville, G. (2006). "ACENTRIC FACTOR". A-to-Z Guide to Thermodynamics, Heat and Mass Transfer, and Fluids Engineering. doi:10.1615/AtoZ.a.acentric_factor.
- Yaws, Carl L. (2001). Matheson Gas Data Book. McGraw-Hill.