Ask A Scientist Chemistry Archive

From:       rbusch
Text:       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.

Response #:  1 of 1
Author:      Robert Topper
Text:        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.