Phase Change and Chemical Potential Energy

1. There is chemical potential energy in the weak van der Waals bonds as well as in the strong ionic and covalent bonds.
2. Because the van der Waals bond/attraction is so much weaker there is much less chemical potential possible here, but it is a major factor in the energy of phase changes.
3. As you can see below, the chemical potential energy of water is less than that of water vapor (or steam) which helps to explain why steam burns can be so severe. Not only is the steam hot, but it tends to condense into a liquid when it touches something. When forming a liquid the chemical potential energy that is released when the van der Waals bonds form can add substantial heat energy to the process of heat transfer from the water molecules to whatever they are condensing on.
4. See a diagram of the energy below:
   
5. A process that releases chemical potential energy as heat is called exothermic.
6. A process that absorbs heat to increase chemical potential energy is called endothermic.
7. Whenever a change of state occurs energy is either absorbed or released
   1. An exothermic process releases heat (converting some of its chemical potential energy to heat energy).
   2. An endothermic process absorbs heat (converting some of the heat energy into chemical potential energy.)
8. Below is a table of common phase changes and their associated energy

   Process	Name of phase change	Energy flow
   solid -> liquid
   liquid -> solid
   liquid -> gas
   gas -> liquid
   solid -> gas
   gas -> solid

9. In endothermic phase changes the energy is used to overcome the weak intermolecular bonds.
10. In exothermic phase changes some chemical potential energy is released as heat energy when the weak intermolecular bonds form.

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