Why does evaporation cause cooling?

• A. Because the liquid absorbs energy from the surroundings
• B. Because the liquid's molecules move faster but heat remains
• C. Because water particles take away thermal energy from the liquid.
• D. Because energy is added to the liquid

Answer: (C)

Evaporation cools because the molecules that escape the liquid surface are the ones with the most kinetic energy. When these high-energy molecules leave as vapor, they take their energy with them, so the liquid loses energy. With less energy available, the average kinetic energy of the remaining molecules drops, and the temperature decreases. The energy required to vaporize those molecules comes from the liquid itself, which is why the liquid cools as evaporation proceeds.