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Crystalline Solids and Lowest Energy
Name: Maggie
Status: student
Grade: 9-12
Country: Malaysia
Date: Fall 2011
Question:
Why does crystalline solid has to be in the lowest energy state?
Replies:
Maggie,
My first thought upon reading your question was: "... lowest energy
state - relative to what?"
The problem is that yes, crystalline solids have lower energy states
compared to the same substance at higher temperatures and different
states, but it may also be of a higher energy state relative to
other substances at the same temperature.
So, maybe let us look at what "crystalline solid" means - and then
you can answer the question based on whatever parameters you want to apply.
By "solid" we mean that the atoms that make up the substance do not
have translational motion. Meaning to say, they may vibrate in
place, but on average stay in the same location. This means that
there is a higher level of order (lower level of entropy) in solids
compared to other phases (liquids and gases) that do have
translational mobility. For this reason, when compared to other
states, we say solids - everything else being equal - have a lower
energy state.
By "crystalline" we mean that the atoms that comprise the solid are
very regularly spaced. This means that solids that are not
crystalline have more disorganization (and likely more translational
mobility) than crystalline solids. It is likely than that there is
less stored energy in crystalline solids than in noncrystalline solids.
Of course, all these statements rely on a careful statement of what
is held constant in the comparison. So, you need to carefully state
that for yourself when making such comparisons.
Greg (Roberto Gregorius)
Canisius College
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Update: June 2012
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