Which symbol is used to denote the gas compressibility factor?

• A. Z
• B. R
• C. P
• D. T

Answer: (A)

The symbol for the gas compressibility factor is Z. It’s a dimensionless quantity that shows how much a real gas deviates from the ideal gas law. For one mole of gas, Z is defined as Z = PV/RT, where P is pressure, V is volume, T is temperature, and R is the gas constant. If the gas behaved ideally, Z would be exactly 1 under all conditions; real gases differ from this, so Z can be slightly less than or greater than 1 depending on the temperature and pressure. At typical low pressures and high temperatures, Z is often close to 1, while at high pressures or near phase transitions, deviations become more pronounced due to intermolecular attractions and repulsions. This makes Z a useful concept in engineering calculations and petroleum context, where the behavior of real gases needs to be accounted for.