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Name: Unknown
Status: student
Grade: 6-8
Location: VA
Country: N/A
Date: 12/29/2004


Question:
Is the process of sublimation endothermic?


Replies:
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.

Vince Calder



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