Phase change when heat is added to a liquid?

• A. Freezing
• B. Condensation
• C. Evaporation or boiling (liquid → gas)
• D. Sublimation

Answer: (C)

When heat is added to a liquid, its molecules gain energy. As this energy increases, molecules at the surface can break free and become a gas, which is evaporation; and if the liquid reaches its boiling point, vigorous bubbling occurs throughout and it becomes a gas, which is boiling. Both are the phase change from liquid to gas.

This isn’t freezing (liquid to solid, which happens when heat is removed), condensation (gas to liquid, occurs on cooling), or sublimation (solid to gas, skips the liquid). The process described by adding heat to a liquid is evaporation/boiling. Everyday example: boiling water on a stove turns into steam.