Definition: If you have a kettle full of water and bring it to the boil you will see lots of steam coming out the spout. That's evaporation. The water molecules can move easily in the liquid, but they are quite close to each other. As the molecules get more heat energy they move much faster and move apart, right up into the air as they change to gas. This is evaporation when a liquid changes into a gas.
reproduced by permission from Hodder