Sunday, 22 April 2012

Anomalous Expansion Of Water

                                                 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.

                                                    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.

10 comments:

  1. very informative but i think that it could be much more informative

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  2. Water is different. With most everything on Earth except freshwater, the colder it gets, the more dense it becomes. Take alcohol for instance. If we were to fill up a 1 liter container with pure alcohol at 30 degrees Celsius (86 Fahrenheit) and then take another 1 liter container and fill it with pure alcohol at 10 degrees Celsius (50 Fahrenheit) the cooler container of alcohol would weigh more. This is because the cooler alcohol is more dense, so more alcohol molecules can fit in the same container. This is true with freshwater too, up to a point. But at about 4 degrees Celsius (40 Fahrenheit) water reaches its densest point. Amazingly, as water cools further, it actually becomes less dense.

    Each water molecule is made of 2 hydrogen atoms and 1 oxygen atom. These are connected to one another by very strong chemical bonds called covalent bonds. Water molecules are connected to each other by much weaker chemical bonds called hydrogen bonds between the positively charged hydrogen atoms, and one negatively charged oxygen atom in a neighboring water molecule.

    As water gets colder than 4 degrees Celsius (40 Fahrenheit) the hydrogen bonds connecting different water molecules adjust to keep the negatively charged oxygen atoms apart. This results in a crystal latice which begins to form at less than 4 degrees Celsius. This crystal latice is completely formed at freezing, and is commonly known as ice.

    So, why does ice float? Like most things that float, ice floats because it is less dense than liquid water. Ice is about 9% less dense. When ice forms, it takes up about 9% more space than it did as a liquid. Thus, a 1 liter container of ice weighs less than a 1 liter container of liquid water, and the lighter material floats to the top. As we said, water is different............... 0:-)

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  3. thanks but if you can explain it more then it would help me mre

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  4. i merely think that understanding this concept only can prove a great help......you can go to this
    http://www.allaboutwater.org/water-facts.html also
    thanks for reading my comment

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