Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It indicates how volatile a substance is.
5 Must Know Facts For Your Next Test
Vapor pressure increases with temperature.
When vapor pressure equals atmospheric pressure, the liquid boils.
Substances with high vapor pressures at room temperature are considered volatile.
Vapor pressure is independent of the volume of the container but depends on temperature and nature of the liquid.
Raoult's law relates vapor pressure to the mole fraction in ideal solutions.
$$P_{solution} = X_{solvent} \cdot P^0_{solvent}$$, where $$P_{solution}$$ is the vapor pressure of the solution, $$X_{solvent}$$ is the mole fraction of the solvent, and $$P^0_{solvent}$$ is the pure solvent's vapor pressure.