why does the ice expands when it reaches -4 degree Celsius?

Answer 1

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It's because of hydrogen bonding. The little molecules need to line up when they freeze (see crystallize answer above).

Look here:

http://en.wikipedia.org/wiki/Hydrogen_bond

There are fun pictures and info.

Answer 2

4 degrees Celcius is the temperature that water is most dense. This is why ice formed at 0 degrees C floats. The molecules have to line up to form crystals, and are closer together at 4 degreesC.

Answer 3

Water is the only known object to man that expands as it gets colder and shrinks when it gets warmer. The colder the ice gets, the more it expands. That's why when you leave a bottle of water in the freezer, the bottle breaks and cracks from the expanding ice inside.

Answer 4

Ice is solid form of Water.

Water is made of H-O-H bondings or hydrogen bondings which is the reason for its high boiling point.

Hydrogen bondings determine the density of water and it varies with temperature.

Water is less dense at 100oC and highly dense at 4oC but again becomes less dense towards 0oC and loosens due to formation of crystals by the molecules due to hydrogen bonding.

This property makes its molecules loosen up and hence it expands.

Source(s): Me. I am doing research in hydrogen bonding on how to use this bonding energy for useful purposes