Which term describes vaporization of a liquid that occurs at the surface into a gaseous phase not saturated with the evaporating substance?

• A. Boiling
• B. Sublimation
• C. Evaporation
• D. Condensation

Answer: (C)

Evaporation is the vaporization that happens at the surface of a liquid into a gas that is not saturated with the evaporating substance. In evaporation, molecules at the surface gain enough energy to overcome intermolecular forces and escape into the air, even when the liquid’s temperature is below its boiling point. This differs from boiling, which occurs throughout the liquid when its vapor pressure reaches the surrounding pressure and bubbles form inside the liquid. Sublimation is a solid turning directly into gas, and condensation is a gas turning into liquid. Because the surrounding gas is not saturated, it can take on more vapor, allowing evaporation to continue. Factors like higher temperature, larger surface area, and airflow over the surface speed up the process.