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Why Does Water Expand When It Freezes

Updated on October 24, 2012

Why Does Water Expands Upon Freezing?

It is generally accepted that as heat is taken out, there is less kinetic energy to cause vibrations and in turn, the molecule becomes smaller when it freezes. However, the water molecule is an exception and has marveled many scientists in the past.

Water is normally connected in the shape of a V. However, the structure of water becomes a hexagon upon freezing. This is due to the characteristic of the 2 hydrogen bonds that exist in the water molecule.

Water In It's Liquid State

Water In It's Frozen State (Ice)

Due To Density Of The Water Molecule

The strength of the hydrogen bond increases proportionally to a decrease in temperature. The molecules move slower and slower as the temperature is lowered.

As a result, the strength of the hydrogen bond is stronger than energy required to dislocate the hydrogen bond. The structure becomes very sparse and becomes a crystalline solid.

In the case of a water molecule, instead of being tightly packed together as the temperature drops, water in it's frozen state in fact expands in size. The density of the frozen water molecule is therefore less dense compared to water in it's liquid state.

This explains why water expands when it freezes, and also as to why ice is less dense than water, and is able to float on water.


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      Ashley 4 years ago

      It saved me, during my homework!!! Thanks so much.

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      cristianneacsu 5 years ago from Bucharest, Romania

      Reminded me about school and science, nice memories... thank you.