Why water has maximum density at 4 degree celcius
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[edit] Introductory Note
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A chemist's view of the world is not as narrow as one might think! Yes, we start with the atom, and then go on to the rules governing the kinds of structural units that can be made from them. We are taught early on to predict the properties of bulk matter from these geometric arrangements.And then we come to H2O, and are shocked to find that many of these predictions are way off, and that water (and by implication, life itself) should not even exist on our planet! But we soon learn that this tiny combination of three nuclei and ten electrons possesses special properties that make it unique among the more than 15 million chemical species we presently know. When we stop to ponder the consequences of this, chemistry moves from being an arcane science to a voyage of wonder and pleasure as we learn to relate the microscopic world of the atom to the greater world in which we all live.
[edit] Reason
The high density of liquid water is due mainly to the cohesive nature of the hydrogen-bonded network, with each water molecule capable of forming four hydrogen bonds.This reduces the free volume and ensures a relatively high-density, partially compensating for the open nature of the hydrogen-bonded network. Its density, however, is not as great as that of closely packed, isoelectronic, liquid neon (1207 kg m-3 at 27 K, with molar volume 92.8% of water).
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The density maximum ensures that the bottoms of freezing freshwater lakes generally remain at about 4°C and unfrozen. The change in density with temperature causes an inversion in cold water systems as the temperature is raised above about 4°C. Thus in water below about 4°C, warmer water sinks whereas when above about 4°C, warmer water rises. As water warms up or cools down through 4°C, this process causes considerable mixing with useful consequences such as increased gas exchange.
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- Did you know there are approximately 10,000 thunderstorms every day throughout the world? You will learn that the energy released during a thunderstorm can equal that of a nuclear bomb. Lightning has the power to create nitrogen in the atmosphere and rain drives nitrogen into the soil without which the plant world would be unable to produce food for the animal kingdom. Even the beginning of our food chain, the diatom, began in water. And rainbows, what precisely are they?
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[edit] References
1. H2O
