What is molar volume? Solved examples
written by Adeel AbbasThe volume occupied by one mole of gas under standard conditions of temperature and pressure, i.e., STP conditions (0°C and 1 atmosphere i.e., pressure) is called the molar volume of the gas. Its value is 22.414 dm3 at STP.
This volume of 22.414 dm3 is called molar volume and it is true only when the gas is ideal.
Molar Volume Formula
The Molar volume is directly proportional to molar mass and inversely proportional to density. The formula of the molar volume is expressed as
Vm=Molar mass/Density
Where Vm is the volume of the substance.
The standard temperature used is 273 Kelvin or 0oC,
The standard pressure is 1 atmosphere, i.e., 760 mm Hg.
Experimentally, one mole of any gas occupies a volume of 22.4 liters at STP. The equation can be expressed as
1 mole of gas at STP = 22.4 litres of gas.
Solved example 1
Calculate molar volume for a sample of the molar mass of the N2 if the density of the gas is 1.250 g/L.
Solution:
Vm=Molar mass density
The molar mass of Nitrogen = 28.01 g/mol
Vm = (28.01)/(1.250)
Vm = 22.408 L
With the help of this information, we can convert the mass of gas at STP into its volume. We can say that
2.016 g of H2O =1 mol of H2 = 6.02×1023 molecules of H2 = 22.414 dm3 of H2 at S.T.P.
16 g of CH4 = 1 mol of CH4 =6.02×1023 molecules of CH4 = 22.414 dm3 of CH4 at S.T.P.
It is very interesting to know from the above data that 22.414 dm3 of each gas has a different mass but the same number of molecules. The reason is that the masses and sizes of the molecules don’t affect the volumes.
Normally, it is known that in the gaseous state, the distance between molecules is 300 times greater than their diameters.
FAQs
What is the molar volume in SI units?
SI unit: cubic meter per mole (m3/mol).
Why is molar volume important?
It is a useful quantity to “think about” things from a molecular perspective. As all gases that are behaving ideally have the same number density, they will all have the same molar volume. At STP this will be 22.4 L. This is useful if you want to envision the distance between molecules in different samples.
What are STP and molar volume?
Standard temperature and pressure (STP) are defined as 0oC (273.15K) and 1atm pressure. The molar volume of a gas is the volume of one mole of a gas at STP. At STP, one mole (6.02×1023 representative particles) of any gas occupies a volume of 22.414 dm3.
Why are 22.4 liters called the molar volume of a gas?
The molar volume of a gas is the volume of one mole of a gas at STP. At STP, one mole (6.02 × 1023 representative particles) of any gas occupies a volume of 22.4 L. A mole of any gas occupies 22.4 L at standard temperature and pressure (0°C and 1 atm).
What is molar volume dependent on?
The molar volume is usually given for a solid substance at 298.15 K (temperature of standard state). Apart from temperature and density, it depends on the phase and allotrope of the substance.
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