Ask A Scientist Chemistry Archive

  
name         Rodney H.
status       educator
age          60s

Question -   How much in percent will a given volume of water expand
for every 20 degrees Fahrenheit it rises in temperature?
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Check out the web site: http://www.simetric.co.uk/index.htm
and on the right hand column click "specific gravity water" scroll down and
you will find the data you need.

Vince Calder
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Rodney -
  Sorry, you cannot get a one number answer, because the density versus temperature 
  is not a straight line.
It is a curve, almost a parabola.
Liquid water has its maximum density at 3.98 degrees C, and expands for BOTH hotter 
and colder!
At exactly 3.98 degrees C, the thermal expansion coefficient of water is actually 
zero.

Easy places to see this curve are:
http://www.ucdsb.on.ca/tiss/stretton/chem2/data19.htm
http://tidepool.st.usm.edu/crswr/ice.html

One property of a parabola is: its slope is proportional to your distance from the 
level point in the middle.
So your "percent expansion per 20degF"
is less than 0.1% near freezing, rising to almost 0.8% near boiling.
The total expansion, from freezing to boiling, is 4.3%.
You will have to figure out your most useful way to think about this variable 
expansion coefficient.

I found that curve-fitting it with a power of roughly 1.75 works better than a power 
of 2 (a pure parabola).

Jim Swenson
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