Why the density of water is highest at 4 degree celsius?
The answer that you’re looking for is water has very strong hydrogen bonding that creates structure in the molecules. Liquids that do not possess hydrogen bonding generally exhibit increasing density as temperature decreases as molecules pull tighter together. At temps below 4C, water begans to exhibit orientation due to hydrogen bonding. This network expands the volume of the liquid resulting in lower density. That said, there is a misconception that ice has lower density than liquid water. That depends on the ice. Ice can take many crystalline forms depending on temperature and pressure. And there are some structures that have higher density than liquid water. http://en.wikipedia.org/wiki/Ice Ice III at 300 MPa and 250K has a density = 1.16 g/cm^3 Ice X has a density = 2.51 g/cm^3 and even some “non crystalline” forms of ice have higher density than liquid water…
