The perfect gas law is of the greatest importance in physical chemistry because it is
used to derive a wide range of relations that are used throughout thermodynamics.
However, it is also of considerable practical utility for calculating the properties of
a gas under a variety of conditions. For instance, the molar volume, Vm =V/n, of a perfect
gas under the conditions called standard ambient temperature and pressure
(SATP), which means 298.15 K and 1 bar (that is, exactly 105 Pa), is easily calculated
from Vm = RT/p to be 24.789 dm3 mol−1. An earlier definition, standard temperature
and pressure (STP), was 0°C and 1 atm; at STP, the molar volume of a perfect gas is
22.414 dm3 mol−1.