In: Chemistry
Why water expands when it freezes?
Most of the liquids have a normal behavior that when they are cooled, they contracts. at this stage the molecules move slower and they are less able to overcome the attractive intermolecular forces among the molecules makes them to be closer to each other. Once the freezing point is reached, substance solidifies, which causes it to contract further more (crystalline solids are usually tightly packed).
Because of exceptional behavor of Water, When liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes it expands by approximately 9%. (See wikipedia)
I would suggest you to see the phase diagram of water so that you will have clear idea of different states of water at different temperatures and pressures.