Themes > Science > Chemistry > Inorganic Chemistry > More Information About Gas Laws > Gas Index > Density

The ideal gas law can also be used to easily compute the density of a gas. If we look at the expression for the molar mass of a gas, M
M = mRT/PV
we can see the term m/V, mass divided by volume, on the right. Simply substitute d = m/V and solve for d
d = MP/RT

Example: What is the density of oxygen gas at 25oC and 1.00 atm pressure?

Solution: The molar mass of oxygen gas, O2 is 32.00 g/mole. Use the above equation, being careful to use the value of R in the correct units and converting the temperature to Kelvin.

d = MP/RT
d = 32.00 g/mole * 1.00 atm/0.0821 (L*atm/mol*K) * 298 K
d = 1.31 g/L


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