Real Gas
An actual gas whose behaviour deviates from the ideal gas law because its molecules occupy volume and attract one another.
Formula / equation
Z = pV / nRT ≠ 1
Unit
Dimensionless
In depth
At high pressure the finite molecular volume makes the gas less compressible than predicted, giving Z above one; at moderate pressure and low temperature, attractions reduce the pressure exerted and give Z below one. Deviations are largest near the point of liquefaction.
Examples in the real world
Carbon dioxide deviates strongly near 31 °C, which is why it liquefies easily in a fire extinguisher cylinder.