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I tell my students that steam burns at 100°C are more harmful than
water burns at 100°C because the steam has more internal energy
(latent heat --mL). Similarly, water at 0°C has more internal energy
that ice at 0°C. Phase changes (+Q) increase the internal PE of the
atoms, but not the KE (since the temperature does not change).
So here's my dilemma. How do you discuss this conceptually to
students, especially when talking about water? Ice is clearly LESS
dense than water because of its expansion (increased volume) upon
freezing. But if water at 0°C has more internal energy, the WATER
molecules be farther apart and thus become less dense. But they're
not! What causes this?
I'm looking for an "easy" explanation for my students to understand
that the expansion has LESS internal energy.
For all other substances, the solids are MORE dense than theliquids.
Water is a most unusual substance!