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Latent Heat of Fusion & Internal Energy

  1. Nov 8, 2014 #1
    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. jcsd
  3. Nov 9, 2014 #2
    The intermolecular forces between particles in a solid, liquid or real gas are electric in nature. For any two particles, one can assign a potential energy function which increases in magnitude with the product of the charges and decreases in magnitude with the distance between the two particles. "Latent heat" increases the separation between particles, and since the forces are attractive (negative potential energy), this brings about an increase in potential energy (more positive, but a smaller absolute value). Bear in mind that this is an oversimplified model, though.
  4. Nov 9, 2014 #3
    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).
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