Molar Volume

In-depth explanation of Molar Volume

The molar volume of a gas is the volume occupied by one mole of gas at a specified temperature and pressure. For an ideal gas at STP (0°C and 1 atm) it is 22.414 L/mol, which follows from V = nRT/P. This constant is the bridge between gas volume and amount of substance in stoichiometry problems. Real gases have slightly different molar volumes, especially at high pressure or low temperature, because their molecules have finite size and attract one another. The value depends on conditions, so it must always be quoted with the stated temperature and pressure.

Going deeper: Molar Volume

Key ideas: Use V_m = RT/P to find it under any conditions: 22.41 L at 273.15 K and 1 atm, 24.47 L at 298.15 K and 1 atm. In stoichiometry, divide the gas volume by V_m for moles. Liquids and solids have molar volumes of only tens of cm3 per mole, such as 18 cm3 for water.

Common mistakes and connections: Applying 22.4 L/mol to a liquid or solid is a typical error, as is using it for gases away from 0 C and 1 atm. Another is mixing up molar volume with molar mass divided by density for gases at non-standard conditions. It follows from Avogadro's law and the ideal gas law, and it shrinks in real gases at high pressure.

Visualization of Molar Volume

One mole of any ideal gas has the same volume at given T and P: 22.4 L at 273 K and 1 atm, 24.5 L at 298 K and 1 atm. The interactive lesson shows this as a live animation or chart.

Worked example and use case

A sample of 11.2 L of any ideal gas at STP contains 0.5 mol of gas.

Where Molar Volume fits in States of Matter & Solutions

Molar Volume is topic 25 of 109 in States of Matter & Solutions.

Related topics

• Root Mean Square SpeedIntermediate
• Maxwell-Boltzmann DistributionIntermediate
• Average Kinetic Energy of GasIntermediate
• Gas DensityIntermediate
• Gas StoichiometryIntermediate
• Real GasesIntermediate

Browse all 109 topics in States of Matter & Solutions