Mole Fraction
The ratio of the moles of one component to the total moles of all components in a mixture.
Formula / equation
x_A = n_A / n_total
Unit
Dimensionless
In depth
Mole fractions are dimensionless, sum to exactly one across all components, and are independent of temperature. They appear directly in Raoult's law and in Dalton's law of partial pressures, which makes them the natural concentration unit for solution and gas-phase thermodynamics.
Examples in the real world
Mixing 1 mol ethanol with 4 mol water gives x_ethanol = 0.20 and x_water = 0.80.