Acentric factor
Encyclopedia
The acentric factor 
is a conceptual number introduced by 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.The a-centric factor is said to be a measure of the non-sphericity (centricity) of molecules.
It is defined as:
.
where
is the reduced temperature,
is the reduced pressure saturation of vapors
.
For many monoatomic, 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 gas
es argon
, krypton
, and xenon
.
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:
All fluids at any
-value, in 
conditions, have about the same 
-value, and same degree of convergence.
is a conceptual number introduced by 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.The a-centric factor is said to be a measure of the non-sphericity (centricity) of molecules.It is defined as:
.where
is the reduced temperature, is the reduced pressure saturation of vaporsVapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
.
For many monoatomic, 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 gasNoble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...
es argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, krypton
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
, and xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
.
Experimental data yields compressibility factors for all fluids that are correlated by the same curves when
(compressibility factorCompressibility factor
The compressibility factor , also known as the compression factor, is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behavior. In general, deviation from ideal behavior becomes more significant the closer a gas is to a phase change, the lower the...
) is represented as a function of
and . This is the basis premises of three-parameter theorem of corresponding states:All fluids at any
-value, in conditions, have about the same -value, and same degree of convergence.