Unit #7 CALCULATIONS BASED ON FORMULAE

7.6 - Molar Volume of a Gas

When the molar mass of ANY gas is divided by the density of gas at STP, the value 22.4 is obtained.

Here are some examples:

Gas Molar Mass (g/mole) Density at STP (g/L) Molar Mass/Density (L/mole)
N2, nitrogen gas
28.014
1.25
22.4
O2, oxygen gas
31.998
1.43
22.4
CH4, methane gas
16.043
0.714
22.4
CO2, carbon dioxide
44.009
1.96
22.4
H2, hydrogen gas
2.015
0.090
22.4
Ar, argon gas
39.948
1.78
22.4

Let's take a look what the units of "22.4" is by dimensional analysis (see Section 1.4).

'22.4' has units of liter/mole. This quantity is known as the molar volume of a gas at STP. When 1 mole of gas is at 0oC and 1 atm (or STP condition), the volume that the gas occupies is always 22.4 liter.

 


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