Molvolumen

Molvolumen, also known as molar volume, is the volume occupied by one mole of a substance. It is defined as Vm = V / n, where V is the volume and n is the amount of substance in moles. For a pure substance with density ρ and molar mass M, Vm = M/ρ, showing how density fixes the molar volume in condensed phases.

In gases, Vm is described by the ideal gas law: Vm = RT/P. At standard pressure (1 atm) and 0°C, Vm,ideal = 22.414 L/mol; at 25°C, Vm,ideal ≈ 24.465 L/mol. Real gases deviate from this value, with deviations described by the compressibility factor Z = PV/(nRT), which depends on temperature, pressure, and molecular interactions.

For condensed phases, Vm is typically much smaller. Example: water, M = 18.015 g/mol and density ≈ 1.0 g/mL at near room temperature, gives Vm ≈ 0.018 L/mol. Diamond, with M = 12.01 g/mol and density ≈ 3.51 g/cm^3, yields Vm ≈ 3.42 cm^3/mol. Liquids and solids generally show weaker variation of Vm with temperature than gases, but Vm does change with temperature and pressure due to thermal expansion and compression.

Applications of molvolumen include calculating material volumes from mass, using it in equations of state, and analyzing phase equilibria. The concept extends to partial molar volume, which describes how the volume changes when a component is added to a mixture.