NGA 70 Properties of Natural Gas and Abnormal Operating Conditions Practice Test

Compressibility factor Z accounts for how real gas behavior deviates from the ideal gas law in gas flow calculations. In the ideal gas law, PV = nRT, but real gases at pipeline conditions don’t follow this exactly because of molecular interactions and finite molecular size. Z captures those deviations, so we rewrite the equation as PV = ZnRT (or Z = pV/RT for a mole). Using Z lets you keep using the familiar form of the gas law while incorporating how the gas actually behaves, which leads to more accurate results for volume, flow rates, and energy calculations. If Z is less than 1, the gas is more compressible than the ideal model under those conditions; if Z is greater than 1, repulsive forces dominate and the gas behaves less compressibly. The other choices don’t fit because Z does not ignore real gas effects, it accounts for them; it applies to gases, not liquids; and it does not replace pressure but modifies the relation between P, V, and T in the gas law.