# Moist Air - Mole Fraction of Water Vapor

## Mole fraction of water vapor is the ratio of water molecules to air and water molecules.

The mole fraction of water vapor is the ratio of the number of mole of water vapor in the moist air - to the total number of mole of dry air and water vapor.

The mole fraction of water vapor in moist air can be expressed as

x_{w}= n_{w}/ (n_{a}+ n_{w})(1)

where

x_{w}= mole fraction of water vapor

n_{w}= mole of water

n_{a}= mole of air