# Latent Heat of Fusion & Internal Energy

1. Nov 8, 2014

### Jimmy87

I understand the main concepts around this topic but I am struggling to find any information about the potential energy involved in the latent heat of fusion. My book defines internal energy as kinetic and potential unlike an ideal gas that is assumed to have just kinetic energy. When a substance reaches a phase change, extra energy (latent) goes into breaking the bonds instead of raising the temperature (average kinetic energy). I can't seem to find anything that explains any detail about this potential energy. How is the energy that goes into breaking bonds a potential energy? I always thought potential energy is energy due to position in a force field?

Thanks for any help.

2. Nov 9, 2014

Think of it as a direct consequence of Coulomb's Law. For two charges in free space, $q_1$ and $q_2$, the potential energy is given by:
$U = \frac{1}{4πε_0} \frac{q_1 q_2}{r}$ where r is the separation between the two charges. Note that this equation is sign sensitive; if the two charges are alike, U > 0. If the two charges are opposite, U < 0. We are interested in the latter. Play around with the numbers, and you'll realize that U increases with r (becomes more positive, that is).