Mole fraction

Mole fraction is the amount of one component in a mixture divided by the total amount of all components. It is dimensionless, and the mole fractions of all components sum to one.

Amount of substance: A measure of the number of specified elementary entities in a sample, with the mole as its SI unit. The numerator and denominator are amounts of substance, not masses or volumes.
Mole ratio: A ratio comparing the amounts in moles of two substances. Dividing one component's amount by the total gives its mole fraction; dividing by another gives a mole ratio.
Partial pressure: The pressure a gas component contributes to a mixture under a specified convention or gas model. In an ideal-gas mixture, partial pressure is total pressure multiplied by mole fraction.
Mass fraction: The mass of one component divided by the total mass of a mixture. Components with different molar masses can have very different mole and mass fractions.
Mole: The SI unit of amount of substance, defined by fixing the Avogadro constant at exactly 6.02214076 × 10²³ per mole. Mole fraction compares component amounts commonly expressed in moles.
Avogadro constant: The number of specified elementary entities in one mole, exactly 6.02214076 × 10²³ mol⁻¹. Equal mole fractions correspond to equal fractions of entities when all components use the same entity basis.
Raoult's law: An ideal-solution relation connecting a component's vapor pressure to its liquid mole fraction and pure-component vapor pressure. Liquid mole fractions predict vapor composition and pressure in ideal mixtures.
Volume fraction: The volume of one component divided by the total volume of a mixture, under specified conditions. Mole fraction and volume fraction need not match, especially in nonideal mixtures.
Mixture: A physical combination of two or more substances that retain their chemical identities. Mole fractions describe the composition of mixtures.
Dalton's law of partial pressures: A gas-mixture law stating that total pressure equals the sum of its component partial pressures. For an ideal-gas mixture, each component's pressure fraction equals its mole fraction.

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