What is molar volume?

Molar volume

In the area of ​​chemistry, it is very important to know the volume occupied by substances used for scientific experiments that require extreme precision. Since the mole is one of the seven units of measurement of the fundamental physical quantities of the International System of Units (SI), it is necessary to know the volume that a mole of a substance occupies in order to work with it in the field of chemistry. In the particular case of molecular gases, a mole contains the value of Avogadro’s number (N a ) and, complying with Avogadro’s law, if an ideal gas is in the middle of the same pressure and temperature conditions, the molar volume of this gas will be the same as another ideal gas with the same conditions.

Molar volume

  • Symbol:  V m
  • Unit: L / mol

What is molar volume?

Molar volume is the space occupied by one mole of a substance . This term is used in the field of chemistry to determine the reflected molecular volume in cubic meters per mole (m 3 x mol -1 ) . A mole is the unit contemplated by the International System of Units that allows to measure and express a certain quantity of substance. The molar volume of an ideal gas under normal conditions (1 atmosphere of pressure and 0 ° C of temperature) is equal to 22.4 liters / mol . Molar volume can be calculated for substances in liquid, solid and gaseous states.

It is important to mention that there is a law that determines which are the ideal or perfect gases and the ordinary or imperfect gases in which the value of the molar volume equal to 22.4 liters is not fulfilled . For other substances in solid or liquid state, the molar volume is different and less than that of gaseous substances.

  • What is molar volume used for
  • Symbol
  • Molar volume formula
  • Examples

What is molar volume used for

It is used to know the volume that a substance occupies in a given space . This substance can be in a gaseous, liquid or solid state .


The symbol for molar volume is V m

Molar volume formula

Formula chemistry to calculate the volume is V = M / D . In the case of molar volume, it must be taken into account whether these substances are mixtures of gaseous or non-gaseous elements.

Gaseous substances in the formula is V m = V / N . Where V is the Volume and N is equal to the number mol / gram.

It is important to remember that for calculating the formula N is N = m / M . Where m is equal to the weight of the sample and M is its molecular mass. Another way to calculate N is with the formula N = n ° of molecules / N a. Where N a is Avogadro’s number which is equal to 6.02 x 10 23

In mixtures or non-gaseous substances they are calculated with the formula V m = M (mass expressed in moles) / D (density expressed in cm 3 )


Here are some examples of the molar volume of gas, ethanol, and oxygen.

Example 1: The molar volume of the gas

When determining the molar volume of a gas it is important to know if they are “ideal or perfect” or if they are ordinary gases not perfect .

The ideal gases – according to Avogadro’s law – under normal conditions of pressure (10 ^ 5 pascals) and temperature (273.15 K = 0 ° C) is 22.4 liters . This value is the normal molar volume of a gas.

There is an ideal gas law that allows us to recognize this type of gas.

In the case of ordinary or non-perfect gases, their molar volume deviates slightly from the value of ideal gases. This is the case of gases such as: sulfur dioxide (SO 2 ) which has a molar volume of 21.9 L or carbon dioxide (CO 2 ) with a value of 22.3L

Example 2: molar volume of ethanol

Ethanol (CH 3 -CH 2 -OH) is a substance that has a molar mass of 46.07 g / mol and a density of 0.789 g / cm 3 . This substance is made up of Hydrogen (H) Carbon (C) and Oxygen (O).

The formula for substances is mass / density . In this sense, to know the molar volume of Ethane, this formula is applied with the ethanol values.

Vm = 46.07 g / mol / 0.789 g / cm 3

Vm = 59.188 cm 3 / mol

Example 3: molar volume of oxygen

Oxygen is considered an ideal gas and for this reason its molar volume under normal conditions is 22.4 L per mole. This means that if you want to calculate its exact volume in an amount X of liters of oxygen, you should apply a rule of three like the following:

1Mol —————— 22.4L

X ——————- Number of liters of oxygen that you have.

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