Liquids evaporate into the air when their molecules gain enough energy to break free of the liquid’s surface tension and become a gas. As this happens only at the surface, or liquid-air interface, the amount of surface area a liquid has partially determines its evaporation rate.
If a gallon of water is poured into a small-necked bottle and left uncapped, it will eventually evaporate, and all of the liquid will become water vapor. However, it will take a great length of time because there is not much of the liquid in contact with the air. By contrast, a gallon of water that is poured into a very long, shallow pan will evaporate relatively quickly because a higher percentage of the water is in contact with the air. The large surface area of lakes and oceans allows enough evaporation to form clouds and precipitation.
Surface area is not the only thing that influences the rate of evaporation. The temperature of the water also has an effect on the evaporation rate. Because hot water contains more energy than cold water, the rate at which molecules transition to the gaseous state increases proportionally with the temperature. Water evaporates quickly once the boiling point is reached.