In general, when a pure substance or mixture goes from liquid to solid, the molecules in it get closer resulting in a higher density.

If this is so why does ice float in water?

water reaches its highest post-zero density at about 4 degrees C. At lower temperatures its structure starts to change. in its crystal solid structure the molecules are further apart than they are in liquid form. This is just thermodynamically more stable for water which has some very anomolous properties. Upon more intense freezing ice does eventually conform to standard procedure and become more dense than water. I dont have any actual values or figures and i apologise if my argument is a little bit of a hand-waving one. But hey im only an undergraduate and i have no text books at hand! :)

Posted by ben on 2003-12-10 20:37:01