Question

How does anomalous expansion of water helps in preserving aquatic life !!! Mention the ans with the specific temperature also ?​

Answer 1

$\huge\green{\underline{\mathfrak{Answer}}}$

$\bullet$First, What is Anomalous expansion of water?

= Generally, Liquids expand on heating. Their volumes increase with the rise of temperature. But water deviates within a certain range of temperature. When water is cooled from room temperature, it contracts till the temperature reaches 4°C. Below this temperature water expands with the fall in temperature till 0°C instead of contracting, and water freezes to form ice. This is called anomalous expansion of water.

$\bullet$How does anomalous expansion of water helps in preserving aquatic life?

= This behaviour of water have a great importance to preserve marine life in countries with freezing temperature. When air above the surface of the water body falls below 0°C, as a result it freezes and becomes denser than the water below the surface and gradually sink downwards. It continues till the water temperature falls to 4°C. As the surface temperature falls further it becomes less dense than the water below. The water below at 4°C is the densest. It thus remains at the top cooling more and more and then ice is formed at the surface. The layer of ice prevents the heat from the water below to pass into the upper colder atmosphere. Thus marine life is saved by this peculiar behaviour of water called anomalous expansion.

Answer 2

★ $\textbf{\underline{\underline{Answer :-}}}$

• We know that when a gas is cooled, it liquefies. If the liquid is cooled further it solidifies.

• Similarly, a solid when heated it melts and on further heating changes to gaseous state.

• We also know that the particles in a gas are loosely packed ; they are packed closer in a liquid and are densely packed in a solid.

• Thus as we go on cooling a substance, the volume of the substances is decreased.

• In other words, a substance contracts on cooling. Water is an exception to this rule.

• When we cool water vapour, it condenses to form water. When we go on cooling water till 4°C water again reduces in volume.

• But if we continue cooling water from 4°C to 0°C, the volume of water increases instead of decreasing in other words, water expands on cooling between 4°C to 0 C.

• This behaviour of water is known as the anomalous expansion of water.

• The volume of any quantity of water is lowest at 4°C. The molecules of water are most closely packed at this temperature.

• As the temperature falls further the intermolecular spaces between

the water molecules increase.

• Because of the large intermolecular spaces, ice occupies more space than the same amount of liquid water in other words, ice is lighter than water and hence floats on it.

• In countries with cold climate and in the Polar Regions, the temperature in winters goes well below 0°C.

• If it were not for the anomalous expansion of water, the water in lakes, ponds and rivers would freeze entirely, thus killing the aquatic animals and plants.

• Instead, as the temperature of water falls below 4°C, the top layer of water in a pond contracts, becomes heavier and sinks to the bottom.

• As the surrounding temperature falls beyond 0° C the water on the surface freezes.

• The ice on the surface of the water acts as a barrier for heat.

• Ice being a bad conductor of heat prevents the heat exchange from the inside of the water and the surroundings.

Thus, the temperature below the layer of ice is maintained at around 4°C and the aquatic life can survive comfortably.