States of Water Experiment

Just how does water change from one state to another? It all goes back to the individual water molecules you learned about on the previous page. When water molecules are heated, they get excited and start to move around faster--just like when you get excited and are filled with lots of energy.

Experiment

1. Place a piece of ice on a plate.
2. Place the plate on a windowsill or under another light source.
3. Observe.

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What do you notice about the ice? When water is in the solid state as an ice cube, the water molecules are closely packed together and are unable to move. Once you place the ice cube on the windowsill, you have exposed it to the sun, which is a heat source. The heat from the sun gives the water molecules energy, and they slowly begin to move around and bump into one another. We see this as the ice cube melting into a pool of water. You just observed water changing from a solid to a liquid!

What do you think would happen to the water if we left it on the windowsill for 24 hours? When you return to the plate the next day, you would notice that some or all of the water had disappeared. Where did it go? Again, the heat from the sun gave the water molecules energy as the liquid water began to heat up. The water molecules began to move around even more and bump into each other so much that they eventually floated into the air and became a gas through evaporation, which is the process of a liquid changing into a gas. Water molecules in gas form have the most energy, because they are moving around a lot!

For a liquid to turn back into a solid, the heat energy in the water needs to be removed from the liquid. As the water's temperature drops, the water molecules start to move slower and slower until they lock back together and are unable to move, becoming a solid again, in this case an ice cube. 

The same is true for gas changing into a liquid. As gas water molecules begin to cool, they slow down and move closer to one another until they join up again as liquid water in a process known as condensation.

It’s important to understand how water changes states in order to have a better understanding of the phase changes that occur in the water cycle..