Which statement best describes the effect of evaporation on surface temperature?

• A. Heats
• B. Cools
• C. No change
• D. Warms then cools

Answer: (B)

Evaporation cools surfaces because energy is required to change liquid water into vapor, and that energy (latent heat of vaporization) is drawn from the surface and its immediate surroundings. As water at the surface absorbs heat to evaporate, the surface loses heat faster than it can be replenished, causing the temperature to drop. This is why sweating feels cooling and puddles evaporate and the surface dips in temperature. If evaporation continues, the surface remains cooler; once evaporation slows or stops, the temperature trends back toward the ambient. In infrared practice, moisture or sweat can make a surface appear cooler than it would be otherwise due to this evaporative cooling.