# COMPRESSIBILITY FACTOR

The compressibility factor (Z) or compressibility accounts for non-ideality in pressure, volume and temperature relation of an ideal gas given by the ideal gas law. The ideal gas law is given below:

P.V = n.R.T

where

P is pressure of ideal gas,
V is volume of ideal gas,
n is number of moles of ideal gas,
R is universal gas constant and
T is temperature of ideal gas

Compressibility factor is the ratio of real molar volume of a gas to ideal molar volume of the same gas at same temperature and pressure.

Z = Vm / (Vm)ideal gas

So ideal gas law is modified for real gases by using compressibility factor as given below:

P.V = n.Z.R.T

where

P is pressure of real gas,
V is volume of real gas,
n is number of moles of real gas,
Z is compressibility factor of real gas
R is universal gas constant and
T is temperature of real gas

For a gas that is a mixture of two or more pure gases (air or natural gas, for example), the gas composition must be known before compressibility can be calculated. Compressibility factor values are usually obtained by calculation from equation of state (EOS), such as the Peng-Robinson cubic equation of state, Soave Redlich Kwong cubic equation of state or their variants. Equation of state (EOS), such as the Peng-Robinson cubic equation of state, Soave Redlich Kwong cubic equation of state or their variants can give compressibility factor values for real gases as well as real liquids. Vapour compressibility factor values or gas compressibility factor values can be used to modify ideal gas law for real gases whereas liquid compressibility factor values can be used similarly in place of vapour compressibility factor values to give a useful pressure, volume and temperature relation for real liquids.

EQ-COMP software can be used to give a 250 X 250 matrix of vapour/ gas compressibility factor values and liquid compressibility factor values for a range of up to 250 pressure and temperature points placed at equal intervals. Sample results of vapour/ gas compressibility factor values calculation module are available  at VAPOR COMPRESSIBILITY Z FACTOR CALCULATOR webpage whereas sample results of liquid compressibility factor values calculation module are available at LIQUID COMPRESSIBILITY Z FACTOR CALCULATOR webpage.

Results for vapor/ gas compressibility factor software / calculator and liquid compressibility factor software / calculator can be requested from VLE CALCULATOR page.