Mole Fraction Article Index for
Mole
Website Links For
Mole
 

Information About

Mole Fraction




: x_i \equiv rac{n_i}{n} = rac{N_i}{N}

where

: n = \sum_j n_j \,

The sum is over all components, including solvent in the case of a solution. As indicated above, the same Ratio is obtained using the number of Molecule s of i, N_i, and the total number of molecules of all kinds, N.

:N_i = n_i imes N_A

where N_A is Avogadro's Number ≈ 6.022 x 1023. By definition, the sum of the mole fractions equals one, a Normalization property.

: \sum_i x_i \equiv 1 \,

Mole fractions are one way of representing the Concentration s of the various chemical species. They are an ideal-mixture approximation, and in practice, all measures of concentration must be multiplied by correction factors called Activity Coefficient s in order to yield accurate results. They are sometimes denoted by the lower case Greek letter \chi (''chi'') instead of a Roman x.

All of the preceding numbers are Dimensionless . Other ways of representing concentrations, e.g., Molarity And Molality , yield Dimension al Quantities (per Litre , per Kilogram , etc.). When Chemical formulas seem to be taking the Logarithm s of dimensional quantities, there is an implied ratio, and such Expressions can always be rearranged so that the Argument s of the logarithms are dimensionless numbers, as they must be.

For mixtures of molecules of differing sizes, see: Volume Fraction .


SEE ALSO