Molar Volume Formula

Molar Volume Formula

Molar Volume Formula is the volume total occupied by one mole of a substance, which may be an element or a compound, at a given temperature and Pressure (STP), which is the basic amount of each because the accurate value differs slightly depending upon the location of the experiment. The STP simplifies and generalises it. In 1811, Avogadro postulated that the volumes of all gases are often easily determined. Avogadro’s law states that equal volumes of all gases at an equivalent temperature and pressure contain equal numbers of particles. During this article, students can learn about the molar volume formula, the perfect gas equation, and various other numerically supported molar volumes.

What is Molar Volume?

Molar Volume Formula is proportional to a substance’s molar mass and inversely proportional to its density.The molar volume of a substance is simply its molar mass, which is divided by its density. If the sample is a mixture containing N components, the approximated molar volume can be easily calculated as the sum of the Molar Volume Formula of its individual components, using the density of the mixture. However, many liquid-liquid mixtures, such as pure ethanol and pure water, experience contraction or expansion upon mixing. This effect is often regarded as “excess volume”.

Vm = relative atomic mass X (Molar mass / Density)

Where Vm is the volume of the substance.

More accurate values of real gas Molar Volume Formula could also be obtained by using equations of state like the van der Waals equation developed in 1873, the Redlich-Kwong equation developed in 1949, the Soave-Redlich-Kwong equation developed in 1972, and therefore the Peng-Robinson equation developed in 1976. The legacy of the Molar Volume Formula is important to know to understand how the current Molar Volume Formula came about.

Molar Volume Formula

The molar Volume Formula is directly proportional to the molar mass of a substance, and it is also inversely proportional to its density. The formula of the molar volume is given by:

Vm=Molar mass/Density

Vm is the volume of the substance.

The standard temperature used for the calculation 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 litres at STP. The equation can be expressed as

1 mole of gas at STP = 22.4 litres of gas.

Ideal Gas Equation

For various kinds of ideal gases, the Molar Volume Formula is used for all the perfect gas equations, and this is often a proper approximation for different common gases at different degrees Celsius and pressures. When there is a rearrangement of the perfect gas equation, it can be used for the molar volume of a perfect gas:

Vm = V/n = RT/P

Hence, for a given temperature and pressure, the Molar Volume Formula is the same for all ideal gases and is understood to be completely equal because of the gas constant: R = 0.082057338(47) L⋅atm⋅K−1⋅mol−1, that’s a relative standard uncertainty of 5.7×10−7, consistent with the 2014 CODATA recommended value. The molar volume of a perfect gas at 100 kPa (1 bar) is 0.022710980(38) m3/mol at 0 °C,0.024789598(42) m3/mol at 25 °C.

Solved Examples for the Molar Volume Formula

When sulphur burns in the air, it forms sulphur dioxide. What volume of gas is produced when 1 g of sulphur burns? (ratio of Ar: S is 32.) (We will measure all volumes at STP)


The balanced equation for the reaction is: S (s) + O2 (g) → SO2 (g)

To Get the number of moles from the grams.

32 g of sulfur atoms = 1 mole of sulfur atoms

As a result, 1 g equals 1 32 mole or 0.03125 mole of sulphur atoms.

1 mole of sulphur atoms gives 1 mole of sulphur dioxide molecules.

So, 0.03125 moles of sulphur atoms give 0.03125 moles of sulphur dioxide.

Next, to get the quantity,

1 mole of sulphur dioxide molecules has  a volume of 22.4 at STP

So, 0,03125 moles is equal to a volume of 0.03125 × 22.4 = 0.7 litres at STP

So, 0.7 litres of sulphur dioxide will be produced.

Q] Calculate the quantity of CO2 gas, CO2, occupied by  5 moles of the gas occupied at STP. Use the Molar Volume Formula

Solution: Volume of CO2 = number of moles of CO2× 22.4 L

= 5 × 22.4

= 112 L

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