Question:
One of the laws of thermodynamics states that things become less
ordered over time. If that is true, then why do crystals form? Since
crystals represent an orderly arrangement of atoms, does the formation of
crystals somehow violate the laws of thermodynamics? It seems that most of
the Earth's rocks should be made up of glass rather than crystals, if things
are supposed to become less ordered as time goes by.
Replies:
Thermodynamics says that any CLOSED system will increase its
entropy over time. However, the earth is not a closed system! We are
constantly receiving tons of energy from the sun. So there are plenty of ways
for systems to become more ordered in the earth. Crystals typically are
formed when particular elements or simple compounds in the earth are cooled
very very slowly from initially molten states. Speaking from a molecular
perspective, substances go into various forms driven by two factors; they
would like to increase the entropy AND lower the energy. Crystals are low-
entropy states, but they are also very low-energy states, and these two
aspects generally compete against each other (there are many exceptions, but
this is a decent crude generalization). To sum: only CLOSED SYSTEMS are
guaranteed to increase their entropy over time, and minerals which crystallize
in the earth are not closed systems. The earth itself is an OPEN system.
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