Question

Explain the importance of the property of anomalous expansion of water.

Answer 1

Anomalous expansion of water:

• The density of water is 1 g cm^-3 at 4°C. Normally, substances expand on heating and contract on cooling. Water also contracts on cooling until the temperature reaches 4°C.
• However, on further cooling below 4°C, water expands instead of contracting up to 0°C. At 0°C, water has the maximum volume in the form of ice. This unusual and unique property of water is known as anomalous expansion of water.
• As a result of this property, the density of water is maximum at 4°C. When water is cooled below 4°C, it expands instead of contracting and becomes less dense (or lighter). At 0°C, water freezes to form ice. Due to expansion, the volume of ice at 0°C is more than the volume of water at 4°C. Therefore, the density of ice at 0°C is less than the density of water. That is why ice floats on the surface of the water.

Effects of anomalous expansion of water:

• In cold regions, where the atmospheric temperature falls to 0°C or below, water on the surface of ponds and lakes cools and freezes into ice.
• The frozen ice floats on the surface of the water as the density of ice is less than the density of water.
• As water is a bad conductor of heat, the ice layer prevents the loss of heat from the lower layers of water.
• Thus, water below the layer of floating ice has temperatures greater than 0°C, which helps in the survival of aquatic life present underneath.