Evaporation & Condensation (detailed) — free printable diagram

Evaporation and condensation explained

Evaporation and condensation are the two changes of state that move water between liquid and gas. Heating a liquid gives its particles enough energy to escape as a gas, which is evaporation; cooling a gas takes that energy away so it becomes a liquid again, which is condensation. They are opposites, they are reversible, and between them they drive the water cycle.

Evaporation

Liquid turning into a gas

Condensation

Gas turning into a liquid

Drives evaporation

Heat energy

Causes condensation

Cooling

Both are

Changes of state — reversible, with no new substance made

Everyday evaporation

A puddle drying up, washing drying on a line

Everyday condensation

Mist on a cold window, dew on grass

• Neither is a chemical change. The water is still water throughout; only the arrangement and energy of its particles change, which is why the process can run both ways.
• Evaporation and boiling are not the same thing, and this is the distinction most often lost. Evaporation happens from the surface of a liquid at any temperature; boiling happens throughout the liquid and only at its boiling point.
• Evaporation is faster when it is warmer, windier, or the liquid has a larger surface area. Those three factors make a good fair-test investigation.
• Condensation happens when water vapour meets a surface, or air, that is cold enough. That is why a cold drink makes the outside of the glass wet — the water comes out of the air, not through the glass.
• The two processes together are what the water cycle runs on: evaporation lifts water into the air and condensation forms the clouds that return it.
• Mass is conserved. A puddle that evaporates has not disappeared; the same water is in the air as vapour, invisible because the particles are far apart.