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Compressibility factor
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Z = PV/nRT measures non-ideality.
Z = PV/nRT equals 1 for an ideal gas; Z < 1 where attraction matters, Z > 1 at high pressure where size matters.
Methane at 100 atm: Z ≈ 0.8.
Plot Z vs P to see non-ideality.
In more detail
The compressibility factor Z = PV/(nRT) measures how far a real gas deviates from ideal behaviour. Z equals one for an ideal gas.
Real-world uses
- Gas pipeline calculations use compressibility factors.
- Natural gas engineers correct volumes using Z.
- Engineers check how far a gas departs from ideal behaviour by measuring its compressibility factor.
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Frequently asked questions
What does Z less than one mean?
Attractions dominate, so the gas is more compressible than an ideal gas.
What does Z greater than one mean?
Repulsion from finite molecular size dominates, so the gas resists compression more.
What value of Z means ideal behaviour?
A value of one means the gas behaves ideally, while values above or below one show repulsion or attraction dominating.
Related topics in Kinetic Theory & Statistical Physics
Graham's law of effusion · Real gases · Van der Waals equation · Liquefaction of gases · Microstates and macrostates · Boltzmann distribution