Energy in Liquids vs Solids
When the solid and liquid phases are in equilibrium,
which phase, solid or liquid contains the greater amount of energy?
There is a quantity called "free energy" or "chemical potential"
(different names, essentially the same things though). When two phases or
even three phases (solid, liquid, vapor) are in equilibrium their "free
energy" or "chemical potential" are equal. In fact that is the definition of
phases being in equilibrium. Things get a bit tricky because you might say
that to melt a solid, I have to "add" heat, so the liquid must have the
higher energy. However, that energy "cost" is exactly balanced by an
increase in the "entropy" (roughly the amount of disorder), so all of the
energy you put into melting goes to creating the liquid, hence the
temperature stays constant. Hang in there you asked a very good thoughtful
question. It is just that the "answer" is not so transparent.
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Update: June 2012