Prof Franklin Piens
How come that water evaporates?

In nature, heat from the sun warms water molecules enough to change them into water vapor which rises into the air. More generally, it is the heat from whatever is near the water that causes it to evaporate.

All molecules are vibrating. Even the molecules that make up your body are vibrating. The vibration is so slight that you don't notice. The hotter an object gets, the faster the vibration is. The colder, the slower. That's why when water gets cold, the molecules vibrates VERY slowly and so the water turns to ice, a solid, the particles sticking close together. When in liquid form, the molecules are vibrating moderately, and so, although the liquid stays together, it is "loose". When water gets overly hot, the particles vibrate so fast that they fly apart in all different directions, making the water a gas (the water evaporates in water vapor).

Other than heat and vibration, one factor or property that causes evaporation is what is generally known as Brownian motion. The scientist Robert Brown discovered that the molecules in water (all liquids to some extent) are always in motion. In this process they collide. The collision changes the direction of motion. So there is random motion among molecules. The molecules at the surface when kicked in the right direction escapes into air. This is evaporation. As the temperature of the liquid increases the speed and thus the energy of collision increases and thus the number of molecules escaping into air increases.