What is meant by the vapor pressure of water?

The vapor pressure of water is the pressure exerted by water molecules in the vapor (gaseous) phase when water is in a closed system and at equilibrium with its liquid (or solid) phase at a given temperature. In simpler terms, it is a measure of how easily water molecules escape from the liquid (or solid) surface to become vapor.

Key Points About Vapor Pressure of Water

• Equilibrium: In a closed container, some water molecules leave the liquid to form vapor, while some vapor molecules condense back to liquid. At equilibrium, the rate of evaporation equals the rate of condensation, and the resulting pressure of the vapor is the vapor pressure.
• Temperature Dependence: Vapor pressure increases rapidly with temperature, as more water molecules have enough energy to enter the vapor phase.
• Boiling Point Relation: The boiling point of water is the temperature at which its vapor pressure equals the atmospheric pressure.
• Volatility: A higher vapor pressure at a given temperature means the substance (here, water) is more volatile and evaporates more easily.
• Scientific Importance: Vapor pressure explains phenomena like humidity, boiling, and condensation and is essential in meteorology and physical chemistry.