# Mole Fraction of Water Vapor in Moist Air

## 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