Subsection 10.2.5 Anomalous expansion of water
Normally, substances expand on heating and contract on cooling. Water exists in three phases solid, liquid, and gas. At temperatures below \(0^{o}C,\) water exists as a solid ice, occupying a bigger volume. When heated, it expands like normal solid up to \(0^{o}C.\) It begins melting at \(0^{o}C\) to liquid water without any change in temperature. Melting is accompanied by a decrease in its volume by about \(8\%\text{.}\) As temperature increases above \(0^{o}C,\) water contracts further up to \(4^{o}C\) and occupies the minimum volume at \(4^{o}C\text{.}\) Therefore water has maximum density at \(4^{o}C\) which is about \(1 \,g/cm^{3}.\) Above \(4^{o}C\text{,}\) water expands like any other liquid. This behavior of water is described as anomalous, unusual, irregular, or peculiar behavior of water. The importance of anomalous properties of water can be summarized as:
- During cold weather, the temperature of lakes drops and water contracts, becomes denser and sinks. A circulation of water is thus set up until all the water attain maximum density i.e. at \(4^{o}C\text{.}\) If further cooling occurs (below \(4^{o}C\)), then any water below \(4^{o}C\) will stay at the top due to its lower density. At \(0^{o}C,\) ice forms on top and this acts as an insulator to the layers below. Hence the relatively warm water underneath ice layer can help sustain aquatic life.
- Ice has a slightly lower density than that of water and hence it floats with a small portion above the water surface. The rest and a larger portion of the ice rests under water. This is called an iceberg. Icebergs pose a great danger to ships as the submerged parts cannot be seen easily by navigators.