Why Does Water Show Maximum Density at 277K?

[shaviprem]

i have had this problem for some time. why exactly does water show a maximum density at about 277 K. and is it the only substance to show such a behaviour.

 

[pallidin]

From http://www.simetric.co.uk/si_water.htm

"When water freezes it expands rapidly adding about 9 % by volume. Fresh water has a maximum density at around 4° Celsius. Water is the only substance where the maximum density does not occur when solidified. As ice is lighter than water, it floats."
----------------
Now, I can not speak for the accuracy of that statement, but that's what that link says.

 

[topsquark]

From http://www.simetric.co.uk/si_water.htm

"When water freezes it expands rapidly adding about 9 % by volume. Fresh water has a maximum density at around 4° Celsius. Water is the only substance where the maximum density does not occur when solidified. As ice is lighter than water, it floats."
----------------
Now, I can not speak for the accuracy of that statement, but that's what that link says.

The reason for water's remarkable properties are usually traceable to the fact that it is such a polar molecule. I would imagine that other polar molecular substances might have similar properties. It would be a place to start looking, anyway.

-Dan

 

[Meir Achuz]

i have had this problem for some time. why exactly does water show a maximum density at about 277 K. and is it the only substance to show such a behaviour.

If that were not true, we couldn't go ice fishing.

 

[russ_watters]

?? That is true - the max density is at 4C (277K) and it decreases from there, which makes ice float. That's also what keeps lakes from freezing solid: 4C water being the least dense, sets up a convection, circulating ground heat.

My understanding was that the crystal structure(s) is unique in being less dense than the liquid state and below 4C, the molecules start to line-up, decreasing the density.