What is the process by which water changes from liquid to gas?

Evaporation is the process by which liquid water changes into water vapour, a gas.

It occurs when energetic molecules at a liquid’s surface escape into the air. Because the fastest-moving molecules leave first, evaporation can cool the remaining liquid. This is why perspiration cools the body and why water in a shallow dish disappears faster on a warm, dry, breezy day.

Evaporation can happen below water’s boiling point and does not require the entire liquid to reach a particular temperature. Boiling is different: it occurs throughout the liquid when vapour bubbles form, whereas evaporation is primarily a surface process. Humidity, temperature, wind speed, and exposed surface area all affect its rate.

Evaporation is a major step in the water cycle. Solar energy drives water from oceans, lakes, rivers, and soil into the atmosphere, where it may later condense into clouds and eventually return as precipitation. Plant water loss is related but is more specifically called transpiration.