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Name: Hank
Status: student
Grade: 9-12
Location: MA
Country: USA
Date: Winter 2011-2012

Question:
At normal atmospheric pressure, and at +4 degrees C I have a small column of water - let us say 2mm diameter and 20 mm high. If I cool the column of water I think it will grow taller. When it gets to 0 Celsius I think the water will begin to freeze, and remain at 0 until all the water has frozen. Will the height of the column change during this freezing process? When the water is all frozen, will the column begin to shrink as temp decreases? Or will it expand all the way down to absolute zero? What is the coefficient? 50 x 10(-6) mm/mm per degree C? Or something else?

Replies:
Hank,

If we look at the density of *liquid* water (as for example here http://www.piercecollegeweather.com/water.html), we see that the density of liquid water increases as the temperature decreases until 4degC where the density decreases past 4degC. So, you are right. If you take liquid water below 4degC then the column of water should rise.

However, this graph (also this table http://en.wikipedia.org/wiki/Properties_of_water#Density_of_water_and_ice) is for *supercooled* liquid water. That is, the water is made to remain a liquid during the analysis. When the water freezes at 0degC, the water will have a discontinuity in density, dropping by about 10%, and then the solid water molecules will become locked in place in its crystal lattice.

As for ice, as we can see from this table: http://www.engineeringtoolbox.com/ice-thermal-properties-d_576.html, the density increases somewhat, so we should expect the solid to shrink with temperature.

Greg (Roberto Gregorius) Canisius College


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