7C: Students know energy is released when a material condenses or freezes and is absorbed when a material evaporates or melts.
I'd first like to start with energy being released when a material condenses or freezes. A good simulation of that is when you put water in a freezer. Its a pretty simple experiment. Put a glass of liquid water in a super cold freezer, an
d whala, you get some ice! It happens because cold stuff makes atoms move less. Back to the water, the water molecules just stop moving, changing from the moving liquid water to the slick ice! Yes, feel the ice, it's very cold compared to the water. I found a video here that shows water molecules freezing. Its pretty cool!
Well, whats really happening is as you take energy away, the molecules can't move as much. Think of it like the molecules are getting tired and don't want to move too much. Well, when the molecules move, it turns into a solid. We solid? - ignore the stupid joke...
The next part of the standard that energy is absorbed when a material evaporates or melts. To check that out, first, put your hand over an open flame... Ok, don't do it because thats stupid and dangerous. But, really, you can already feel how hot an open flame is. The flame is the energy that you are going to use. Now, put a pot of room temperature, liquid water on top of the flame. Just wait a while, and soon, you'll see a whole bunch of steam coming out. That steam is actually fast moving water particles moving so fast it moves as a liquid. By adding a whole ton of heat, which you did by putting a pot of water over an open flame, you added energy to the water, boiling it up and turning it into a gas (water vapor). Isn't that amazing!? Well, that just proves that adding heat, or energy, can really change a substance.
What's really happening here is now we made the molecules more energetic by adding energy. It's like a little kid on chocolate! So now that the molecule's running all crazy, it breaks off from its liquidy mass and turns into a gas. Cool aye?!
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