Where are we going with this? Describe the characteristics of solids, liquids, and gases and changes in state at the macroscopic and microscopic levels.
Two Types of Phase Change: Endothermic and Exothermic
Energy is either absorbed or released in a phase change. For example, for a solid to become a liquid, the energy that is absorbed results in the bonds holding the solid together to break. To reverse it, the liquid molecules must give up energy in order for the molecular bonds to "grab" them and force them into the rigid shape of a solid.
There are two different names for the type of phase change depending on if energy is absorbed or given off.:
Endothermic changes (or reactions) take energy IN. The process absorbs energy from it surroundings. Another way to think of this is that energy ENters the system.Exothermic changes (or reactions) give off energy—energy EXits from the system. The process releases energy into its surroundings.
The following phase changes are Endothermic (require energy to be added to the molecules to cause them to change state):
- Melting
- Vaporization
- Sublimation
- Ionization
The following phase changes are Exothermic (the molecules give up energy in order to "settle" into the new state):
- Freezing
- Condensation
- Deposition
- Recombination/deionization
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