Phase Changes
Phase Changes is what happens when matter shifts between solid, liquid, and gas, like ice melting into water.
An ice cube on a warm plate melts into a puddle of water. If you boil that water on the stove, it turns into steam that rises into the air. The same H2O moved from solid to liquid to gas just by adding heat. Take the heat away and the changes reverse — steam condenses, water freezes back to ice.
Explaining phase changes by grade level
Think about an ice cube sitting on a warm plate. It starts hard and cold, then slowly turns into a puddle of water. The ice did not disappear. It changed form. Heat from the plate made the ice soften and flow. If you put that water in a freezer, it turns back into ice again.
Projects that explore phase changes
Some solids skip the liquid stage entirely. Dry ice is frozen carbon dioxide, and at normal air pressure it does not melt — instead it sublimates, changing directly from solid to gas. Press a warm spoon against a chunk and the gas pushes the spoon away, then contact resumes rapidly. That rapid push-and-return produces a singing sound, letting you hear this phase change happening in real time.
At its freezing point, a liquid crosses into solid — that exact temperature marks the phase change. You prepare salt and sugar solutions at four concentrations, place each in a test tube, then set all eight tubes in a salted ice bath. When the first ice crystals appear, you record the temperature. Both solutes push the freezing point below zero, but salt drops it nearly twice as far as sugar at every concentration.
Ice is solid water. When it melts, it shifts to liquid — and that liquid behaves very differently from the solid it was. You freeze water with food coloring into ice cubes, then drop them into a clear jar of cooking oil. As the cubes melt, the colored water becomes liquid. Denser than oil, it sinks, and streams of color swirl downward through the jar.