|MadSci Network: Chemistry|
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. psu.edu/~demark/471/MixingClouds.html And I would also endorse the answer to a question similar to yours that I found on this site: http://www.sci- ctr.edu.sg/ScienceNet/cat_physical/cat_che06725.html
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