Phase Change: Exothermic or Endothermic
Is the process of sublimation endothermic?
Sublimation is the transition of a solid [S] to a vapor [V]. Evaporation
(boiling) is the transition of a liquid [L] to a vapor [V]. Melting
(fusion) is the transition of a solid [S] to a liquid [L]. These are the
most common types of changes of the physical state of a substance, but not
the only ones. In the direction as written above: [S] ---> [V], [L] --->
[V], and [S] ---> [L] all the transitions require the absorption of heat
and so are endothermic. The reverse transitions [V] ---> [S], etc. give off
heat and so are exothermic. Some substances have more than one crystal
structure, or form glasses instead of crystalline solids, and in the case
of hydrogen and helium have weird types of transitions. In these cases it
is not always self evident whether a particular transition process is
endothermic or exothermic.
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Update: June 2012