MadSci Network: Chemistry

Re: Is steam water vapor (gas) or liquid water?

Date: Thu Apr 11 23:13:04 2002
Posted By: Allan Harvey, Chemical Engineer
Area of science: Chemistry
ID: 1015636369.Ch

Shame on those Michigan benchmark people.  I might have expected something 
like that if it had been Kansas ... :-)

Seriously, in science and engineering "steam" refers to water in its vapor 
state.  You boil liquid water, the resulting vapor is "steam."

Having said that, maybe they do have some excuse. It is not uncommon to 
hear the word "steam" applied to the white cloud you see billowing from a 
smokestack, or when you see your breath on a cold day.  That is not really 
proper terminology; this phenomenon is called a "mixing cloud" (and is 
pretty much the same as clouds in the atmosphere).  When you see a mixing 
cloud (which has water vapor and liquid droplets together), you are in 
some sense seeing liquid water, because the vapor is invisible and the 
white you are seeing is from the liquid droplets (if I remember correctly, 
from the light scattering off the droplets).

So, with this colloquial usage of the word "steam," it is not 100% 
indefensible to say that it is liquid, since it is the liquid that causes 
the white cloud that causes people to call it "steam."  But for proper 
scientific and engineering usage (and for a young level where it might be 
too much to go into things like mixing clouds), it is more correct to say 
that "steam" is a gas (or "vapor" would be a good word to teach the kids).

I find an explanation of the mixing cloud phenomenon here: http://www.ems.

And I would also endorse the answer to a question similar to yours that I 
found on this site: http://www.sci-

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