VPatm

VPatm denotes the volume of a gas measured at atmospheric pressure (Patm). It is a context-specific variable used in physics, chemistry, and engineering to distinguish from volumes measured under different pressures.

Patm is atmospheric pressure; at sea level it's about 101.325 kPa, equivalent to 1 atm.

In the ideal gas law, VPatm = nRT/Patm. For a given amount of substance n and temperature T, the volume at Patm can be computed. As a reference, the molar volume of an ideal gas at 298 K and 1 atm is about 24.47 L/mol.

Notation varies; some sources use V_atm or V_Patm; VPatm should be defined in each source. Real gases deviate from ideal behavior at high pressure; at Patm near 1 atm, ideal gas approximation is reasonable for many gases.

In practice, VPatm is used in lab calculations and modelling when it's useful to specify the condition of Patm.