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Name:   Nick
Status:  student
Age:  9
Location: N/A
Country: N/A
Date: 2000


Question:
We are studing physical changes, and chemical changes at school. my daddy told me to ask the teacher if a solid can go right to a gas witout being a liquid first.she said that carbon dioxide can, but not ice. Dad says she is wrong. would you help me with this one. thanks. Nick.


Replies:
Nick,

Your daddy is correct. Whenever a solid goes directly to the gaseous condition -- without first melting -- the process is called sublimation. As you already know, dry ice can do this. So can solid iodine, naphthalene (moth balls), paradichlorobenzene (moth crystals), camphor, menthol, and other compounds as well.

Ordinarily, ice melts before it becomes a gas. Nevertheless, ice can "evaporate"-- sublime -- just as your father says. Though it does not occur all that often, when the humidity is low and the temperature is just below freezing, even snow (which is ice) can also sublime. Ice will sublime if placed in a vacuum, even if the temperature is well below freezing. Your dad is a smart fellow.

Regards,
ProfHoff



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