What is the formula for calculating the pressure of a gas?

1 Answer
Nov 5, 2016

Most gases closely follow an equation of state called the ideal gas law,


It's important to pay attention to the units, however. In strict SI units (highly recommended), express n in moles, R is the universal gas constant #R=8.314 J/(mol-K)#, T is the temperature in Kelvins, and the volume V is in #m^3#. The resulting pressure P will be in Pa.

The other common set of units is where V is in liters (L) and
#R = 0.082054 (L-atm)/(mol-K)#, in which case the pressure is calculated in atm.

0.25 mol of helium gas confined to a 6L vessel at 250K will have a pressure equal to
#P=(nRT)/V = [(0.25mol)(0.082054 (L-atm)/(mol-K))(250K)]/(6L) = 0.855 atm#