Water Damage Restoration Technician (WRT) Certification Practice Test

What is vapor pressure?

1. The weight of water vapor in air

2. The force exerted by vapor molecules

3. The rate of evaporation in water

4. The temperature of a gas

The correct answer is: The force exerted by vapor molecules

Vapor pressure refers to the force exerted by vapor molecules in a closed system when the vapor is in equilibrium with its liquid or solid form. This force arises from the molecules that escape from the liquid or solid phase into the gas phase and is a reflection of the tendency of a substance to evaporate. In a system where a liquid is exposed to its vapor, molecules will move between liquid and gas phases until the rate of evaporation equals the rate of condensation, resulting in a stable vapor pressure. The higher the temperature, the higher the kinetic energy of the molecules, which increases the vapor pressure since more molecules have enough energy to escape into the vapor phase. Understanding vapor pressure is critical in many fields, including meteorology, chemistry, and water restoration, because it influences processes such as drying, evaporation, and the behavior of humidity in the air.