I am looking into whether the melting of ice (or any substance for that matter) at constant pressure and temperature is reversible or irreversible. Different sources say different things, and it may well depend on specific conditions. But is it generally said that melting is reversible or irreversible?
It's irreversible. The reason can be easily understood when you look the molecular properties of water
The presence of a charge on each of these atoms gives each water molecule a net dipole moment. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as hydrogen bonding. The molecules of water are constantly moving in relation to each other, and the hydrogen bonds are continually breaking and reforming at timescales faster than 200 femtoseconds. However, this bond is sufficiently strong to create many of the peculiar properties of water, such as those that make it integral to life.
This hydrogen bonds are mixing the water, and are the reason for the lower volume of fluid compared to ice.
If you have absolute pure water, it will melt in 0 degrees in normal pressure, but you might need to cool it down to -48 degrees celcius to make it solid again. The reason is the ice lattice structure, which needs more volume than the water.
Ofcourse everything is sort of Reversible; it depend's only from definitions. But here I mean with irreversibilty that the we expect the same atom's to take the exact same positions they had before; -this is impossible. As they are not even on same molecules, they were before.
protected by ACuriousMind♦ Nov 28 '17 at 8:46
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