DEFINITION
Water shows unusual expansion.When it is cooled from four degree centigrade to
zero degree centigrade is known as "anomalous expansion of water."
The unusual behaviour of water, when it expands below
4° celsius to 0° is called anmalus expansion of water.
The unusual behaviour of water, when it expands below
4° celsius to 0° is called anmalus expansion of water.
EFFECTS
The anomalous expansion of water helps preserve aquatic life during very cold weather. When temperature falls, the top layer of water in a pond contracts, becomes denser and sinks to the bottom. A circulation is thus set up until the entire water in the pond reaches its maximum density at 4°C. If the temperature falls further, the top layer expands and remains on the top till it freezes. Thus even though the upper layer are frozen the water near the bottom is at 4°C and the fishes etc. can survive in it easily.
SCINTIFIC REASON
Anomalous expansion of water takes place because when water is heated to
277K hydrogen bonds are formed. Though ice is supposed to expand when
it is converted into water, this gradual formation of hydrogen bonds
causes it to contract, i.e. the contraction caused due to the formation
of hydrogen bonds is greater than the actual expansion of ice. At 277K
water has the maximum density because all the hydrogen bonds are formed
by 277K beyond which water obeys the kinetic theory of molecules, an
increase in volume when heated and the reverse when cooled. The same
thing happens in the reverse when water is cooled beyond 277K.
EXAMPLE
If we take a cube of ice at -5°C and heat
it, it expands till ice starts melting. During melting its temperature
remains 0°C but its volume decreases. If heat is continuously supplied
to water at 0°C, it further contracts up to 4°C and then it starts
expanding. Thus water has its minimum volume and maximum density at 4°C.
