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In thermodynamics, the compressibility factor (Z), also known as the compression factor or the gas deviation factor, describes the deviation of a real gas from ideal gas behaviour. It is simply defined as the ratio of the molar volume of a gas to the molar volume of an ideal gas at the same temperature and pressure .
Water: 2.2 GPa (0.32 Mpsi) (value increases at higher pressures) Methanol 823 MPa (at 20 °C and 1 Atm) Solid helium: 50 MPa (approximate) Air 142 kPa (adiabatic bulk modulus [or isentropic bulk modulus]) Air 101 kPa (isothermal bulk modulus) Spacetime: 4.5 × 10 31 Pa (for typical gravitational wave frequencies of 100Hz) [8]
The compressibility factor is defined as = where p is the pressure of the gas, T is its temperature, and is its molar volume, all measured independently of one another. In the case of an ideal gas, the compressibility factor Z is equal to unity, and the familiar ideal gas law is recovered:
Methane vapor pressure vs. temperature. Uses formula log 10 P mm Hg = 6.61184 − 389.93 266.00 + T ∘ C {\displaystyle \log _{10}P_{\text{mm Hg}}=6.61184-{\frac {389.93}{266.00+T_{^{\circ }{\text{C}}}}}} given in Lange's Handbook of Chemistry , 10th ed. Note that formula loses accuracy near T crit = −82.6 °C
compressibility effects; variable specific heat capacity; van der Waals forces; non-equilibrium thermodynamic effects; issues with molecular dissociation and elementary reactions with variable composition; For most applications, such a detailed analysis is unnecessary, and the ideal gas approximation can be used with reasonable accuracy.
F pv: super compressibility factor (often omitted or shown as equaling 1) Example: How many standard cubic feet are in 1 cubic foot of gas at 80 °F and gauge pressure 50 psi? (assuming that there is 13.6 psi atmospheric pressure and ignoring super compressibility)
According to van der Waals, the theorem of corresponding states (or principle/law of corresponding states) indicates that all fluids, when compared at the same reduced temperature and reduced pressure, have approximately the same compressibility factor and all deviate from ideal gas behavior to about the same degree. [1] [2]
The compressibility factor is a dimensionless quantity which is equal to 1 for ideal gases and deviates from unity for increasing levels of non-ideality. [ 9 ] Several non-ideal models exist, from the simplest cubic equations of state (such as the Van der Waals [ 4 ] [ 10 ] and the Peng-Robinson [ 11 ] models) up to complex multi-parameter ones ...