Phase Changes: Practical Examples

Have you ever noticed that when you step out of the pool, you can feel chilly even if the air temperature is hot? You can even develop goosebumps on your skin. This is because as the water molecules evaporate from liquid droplets on your skin to water vapor in the air, they gain energy from your skin. Because your skin is losing energy, you sense that energy loss as cooling.

When water molecules lower their energy state (such as condensation from vapor to liquid), they create bonds between each other. This releases energy, and the environment warms from the energy that the water molecules have lost. A consequence of this might be eyebrow-raising: when you place ice cube trays filled with water in your freezer, your freezer has to work overtime to offset the warming that’s produced as the ice cubes freeze. We think of freezing as a cold process, but it actually generates heat! This is the way temperature works in general: a back-and-forth between heat possessed by the molecules in the air and heat transferred to and from the surroundings.

Ultimately, water’s phase changes and the energy exchanged with the environment provide the basic mechanism by which water creates the weather.

Here’s a quiz to test your knowledge of the relationship between the phase changes of water and the environment:

Please wait…

1. Does the environment gain or lose energy during deposition?

Gain Energy

Lose Energy

N/A

N/A

Question 1 of 6

2. Do the water molecules gain or lose energy during sublimation?

Gain Energy

Lose Energy

N/A

N/A

Question 2 of 6

3. Do the water molecules gain or lose energy during freezing?

Gain Energy

Lose Energy

N/A

N/A

Question 3 of 6

4. Does the environment gain or lose energy during melting?

Gain Energy

Lose Energy

N/A

N/A

Question 4 of 6

5. Does the environment gain or lose energy during evaporation?

Gain Energy

Lose Energy

N/A

N/A

Question 5 of 6

6. Do the water molecules gain or lose energy during condensation?

Gain Energy

Lose Energy

N/A

N/A

Question 6 of 6

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Phase Changes and Clouds

In the atmosphere, there are places where water changes phase most actively…we know them as clouds.  Clouds are regions of tiny liquid droplets and/or ice crystals suspended in the air. Those droplets and ice crystals scatter light, making them appear white. To keep the droplets and ice crystals from falling towards the ground, the air must rise ever so slightly.  Ultimately, clouds produce much of the weather that affects us.

On the next page, we’ll summarize the key takeaways from this post, provide some useful summary graphics, and wrap it up with one last practice quiz. Please advance to the next page using the links below.

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