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

1 Answer
Chuck W.
Nov 5, 2016

Most gases closely follow an equation of state called the ideal gas law,
#P=(nRT)/V#.

Explanation:

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.

Example:
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#

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