Concept

# Mole fraction

Summary
In chemistry, the mole fraction or molar fraction (xi or χi) is defined as unit of the amount of a constituent (expressed in moles), ni, divided by the total amount of all constituents in a mixture (also expressed in moles), ntot. This expression is given below: :x_i = \frac{n_i}{n_\mathrm{tot}} The sum of all the mole fractions is equal to 1: :\sum_{i=1}^{N} n_i = n_\mathrm{tot} ; \ \sum_{i=1}^{N} x_i = 1. The same concept expressed with a denominator of 100 is the mole percent, molar percentage or molar proportion (mol%). 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. The mole fraction is sometimes denoted by the lowercase Greek letter χ (chi) instead of a Roman x. For mixtures of gases, IUPAC recommends the letter y.
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