Vapor pressure

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

1. Vapor pressure increases with temperature.
2. When vapor pressure equals atmospheric pressure, the liquid boils.
3. Substances with high vapor pressures at room temperature are considered volatile.
4. Vapor pressure is independent of the volume of the container but depends on temperature and nature of the liquid.
5. Raoult's law relates vapor pressure to the mole fraction in ideal solutions.

Review Questions

• How does temperature affect vapor pressure?
• What happens when vapor pressure equals atmospheric pressure?
• Explain Raoult's law in relation to vapor pressure.

Related terms

Boiling Point:

The temperature at which a liquid's vapor pressure equals the external or atmospheric pressure.

Volatility: A measure of how readily a substance vaporizes; substances with high vapor pressures are highly volatile.

Raoult's Law:

$$P_{solution} = X_{solvent} \cdot P^0_{solvent}$$, 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.