One of the few exceptions to the direct relationship between temperature and volume is water. When cooling warm water, its volume decreases. This decrease continues until the temperature drops to approximately 4 ° C. At this temperature, water reaches a maximum density and, therefore, the smallest volume. With further cooling of the water below 4 ° C, it begins to expand. This expansion continues until the temperature drops to a triple point (0 ° C). At the temperature of the triple point, liquid water begins to change to a solid state and continues to expand. Upon completion of the change in state, 0.0283 m3 of water is converted into 0.0307 m3 of ice. This increase in volume produces a tremendous force that can blow up pipes and other containers and destroy ships, piers and other objects that are in the water.
Although it seems that the expansion of water contradicts the relationship of temperature and volume, as described above, this is not so. The average distance between the cooling molecules continues to decrease with decreasing temperature, as the kinetic energy decreases, as expected. But there is a physical, and not a thermal expansion, since the water molecules form a crystalline structure. When the hydrogen and oxygen atoms form bonds, they are divided into pairs, one side of the water molecule receiving a slightly higher positive charge than the other. As a result, the molecules act as triangular magnets, in which one side is electrostatically negative and the other side is positive.
In the liquid state, these electrostatic poles attract the charged side of adjacent molecules and the liquid compresses slightly. When the liquid begins to change the state to a solid, the molecules are rearranged, forming a crystalline structure with a lower entropy. A solid structure disrupts the electrostatic attraction between molecules, since it binds them. The distance between the molecules in the crystal structure is slightly larger than in the liquid state, the volume of water increases when the state changes to a solid state. If not for this structure, the volume of water would be greater than the volume of the ice mass equal to that of other substances.