Vapor pressure

Definition

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature. It reflects how readily molecules escape from the liquid or solid phase into the gas phase.

5 Must Know Facts For Your Next Test

1. Vapor pressure increases with temperature, reflecting higher kinetic energy and more molecules escaping into the vapor phase.
2. A substance with high vapor pressure at room temperature is considered volatile.
3. At boiling point, a liquid's vapor pressure equals atmospheric pressure.
4. Raoult's Law states that the vapor pressure of an ideal solution is directly proportional to the mole fraction of solvent present.
5. The Clausius-Clapeyron equation relates vapor pressure and temperature, allowing calculation of enthalpy of vaporization.

Review Questions

• How does temperature affect the vapor pressure of a liquid?
• What condition must be met for a liquid to boil?
• What does Raoult's Law state about the vapor pressure of a solution?

Related terms

Boiling Point: The temperature at which a liquid's vapor pressure equals atmospheric pressure.

Volatility: A measure of how readily a substance vaporizes; high volatility corresponds to high vapor pressure.

Clausius-Clapeyron Equation: An equation that describes the relationship between vapor pressure and temperature for pure substances.