# Mole fraction

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Mole fraction

In chemistry, the mole fraction xi is defined as the amount of a constituent ni divided by the total amount of all constituents in a mixture ntot: $x_i = \frac{n_i}{n_{tot}}$

The sum of all the mole fractions is equal to 1: $\sum_{i=1}^{N} n_i = n_{tot} ; \; \sum_{i=1}^{N} x_i = 1$

The mole fraction is also called the amount fraction. It is identical to the number fraction, which is defined as the number of molecules of a constituent Ni divided by the total number of all molecules Ntot. It is one way of expressing the composition of a mixture in a dimensionless size (mass fraction is another). The mole fraction is sometimes denoted by the lower case Greek letter χ (chi) instead of a Roman x. For mixtures of gases, the letter y is recommended.

## Properties

Mole fraction is used very frequently in the construction of phase diagrams. It has a number of advantages:

• it is not temperature dependent (such as molar concentration) and does not require knowledge of the densities of the phase(s) involved
• a mixture of known mole fraction can be prepared by weighing off the appropriate masses of the constituents
• the measure is symmetric: in the mole fractions x=0.1 and x=0.9, the roles of 'solvent' and 'solute' are reversed.
• In a mixture of ideal gases, the mole fraction can be expressed as the ratio of partial pressure to total pressure of the mixture.

## Related quantities

### Mass fraction

The mass fraction wi can be calculated using the formula $w_i = x_i \cdot \frac {M_i}{M}$

where Mi is the molar mass of the component i and M is the average molar mass of the mixture.

### Mole percentage

Multiplying mole fraction by 100 gives the mole percentage, also referred as amount/amount percent (abbreviated as n/n%).

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### Look at other dictionaries:

• mole fraction — n. the ratio of the number of moles of one constituent of a mixture or solution to the total number of moles of all the constituents …   English World dictionary

• mole fraction — molinė dalis statusas T sritis fizika atitikmenys: angl. molar fraction; mole fraction; molecular fraction vok. Molenbruch, m rus. мольная доля, f; молярная доля, f pranc. fraction molaire, f …   Fizikos terminų žodynas

• mole fraction — molinė dalis statusas T sritis Standartizacija ir metrologija apibrėžtis Tiriamojo sando molių ir visų sistemos sandų molių sumos dalmuo. atitikmenys: angl. atomic fraction; mole fraction vok. Molenbruch, m rus. мольная доля, f; молярная доля, f… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• mole fraction of B — molinė B sando dalis statusas T sritis Standartizacija ir metrologija apibrėžtis B sando ir mišinio medžiagos kiekių dalmuo. atitikmenys: angl. mole fraction of B rus. молярная доля компонента B, f pranc. fraction molaire de B, f …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• mole fraction — molinė dalis statusas T sritis chemija apibrėžtis Tiriamojo komponento molių ir visų sistemos komponentų molių sumos santykis. atitikmenys: angl. atomic fraction; mole fraction rus. атомная доля; молярная доля ryšiai: sinonimas – atominė dalis …   Chemijos terminų aiškinamasis žodynas

• mole fraction — noun Etymology: mole (VII) : the ratio of the number of moles of one component of a solution or other mixture to the total number of moles representing all of the components * * * Chem. the ratio of the number of moles of a given component of a… …   Useful english dictionary

• mole fraction — Chem. the ratio of the number of moles of a given component of a mixture to the total number of moles of all the components. [1920 25] * * * …   Universalium

• mole fraction — noun the ratio of the number of moles of one component of a mixture to the total number of moles …   Wiktionary

• mole fraction — in a system, the ratio of the mass in moles of a component to the mass in moles of all components …   Medical dictionary

• Mole (unit) — This article is about physical quantity measurement unit. For other uses, see Mole (disambiguation). The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains …   Wikipedia