Water cooled/heated between 0 -4 C

[wakejosh]

this may be a silly question but:

I understand that water heated between 0 and 4 C will contract, does this mean that if it is cooled from 4 to 0 C it will expand?

 

[Office_Shredder]

Yes. Ice floats because it's less dense than water... this isn't an instantaneous expansion, it happens over the last couple of degrees, as the water begins to take on icy like structure (or something like that)

 

[americanforest]

Sorry to hijack your thread but I have a similar question: does this work for air as well, ie. is hot air more dense than cold air? Is this why it is cold in the atmosphere and on mountains?

 

[wxrocks]

https://www.physicsforums.com/showthread.php?t=140985&highlight=atmosphere

 

[ThalorB]

I am not familiar with the specifics of the 0-4 C temp. range; but, I assume it is for standard temp. and pressure. The expansion/contraction of water has to do with the bond strength between the molecules - dipoles I believe. When water cools to near freezing, the molecules no longer have enough energy to break free from this bonding force. It just so happens that the when the molecules align in this way to make the ice crystals, they require a larger volume, hence lower density.

This is different from gas/air. Those atoms/molecules have sufficient energy to completely overcome any inter-atomic/molecular forces -> phase change.