Synonym: Mole fraction = Molar fraction

A ratio of amount of a given mixture component to the total amount of substance $\begin{array}{l}\nu\end{array}$ in the mixture:

(1)	$\begin{array}{l}\displaystyle x_i = \frac{\nu_i}{\nu} = \frac{N_i}{N}\end{array}$

where

$\begin{array}{l}\nu_i = N_i/N_A\end{array}$	amount of substance of the $\begin{array}{l}i\end{array}$ -th mixture component
$\begin{array}{l}\nu = \sum_i \nu_i\end{array}$	total amount of substance in the mixture
$\begin{array}{l}N_A\end{array}$	Avogadro constant
$\begin{array}{l}N_i\end{array}$	amount of molecules/atoms in the $\begin{array}{l}i\end{array}$ -th mixture component
$\begin{array}{l}N = \sum_i N_i\end{array}$	total amount of molecules/atoms in the mixture

As per definition the sum of all mole fractions is strictly unit: $\begin{array}{l}\sum_i x_i = 1\end{array}$ .

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