Final answer:
Evaporation is the process where liquid water gains kinetic energy, often from the sun's heat, and changes into water vapor below its boiling point. This is a key part of the water cycle and involves a cooling effect known as evaporative cooling.
Step-by-step explanation:
Understanding Evaporation
When water evaporates, it undergoes a phase change from a liquid to a gas, which is termed water vapor. This process can occur at various temperatures and happens when the water molecules gain enough kinetic energy from external sources, such as the sun, to overcome their intermolecular attractions and escape into the atmosphere. Evaporation is part of the water cycle, which is crucial for sustaining life on Earth. During evaporation, energy is absorbed by the liquid, resulting in the cooling of the remaining liquid; this is why you feel cooler when you sweat on a hot day.
The kinetic energy provided by the sun is essential for evaporation to occur. The sun heats the water, allowing molecules on the surface to gain sufficient energy to transition into the gaseous state and mix with the air as water vapor. Even at temperatures below the boiling point, evaporation happens, although boiling accelerates this process with visible bubbles of gas forming in the liquid.
Relative humidity is an important factor in evaporation as it represents the fraction of water vapor in the air compared to its saturation value. A lower relative humidity facilitates evaporation since the air can hold more water vapor. On the other hand, condensation is the reverse process where water vapor turns back into a liquid, balancing the evaporation in a closed system.