Does hot water freeze faster than cold water?

[twoflower]

Hello,

my colleague told me that he read once somewhere that water freezes more quickly if it is given to frost hot. It is supposed to be caused by tighter organisation of moleculs in a hot water and thus being better prepared for transition into crystalic state of matter.

Is there any truth in this?

Thank you.

 

[Tide]

If that is the case then wouldn't the "hot" water eventually cool to the point where it becomes just as disorganized as the "cold" water started out - and still be behind in its race to freezing?

 

[ZapperZ]

I could have sworn there was at least a thread on this already somewhere, but I couldn't find it. In any case, here's the explanation, and the name for this effect:

http://math.ucr.edu/home/baez/physics/General/hot_water.html

Note the SPECIAL CIRCUMSTANCES to which this effect can be seen. In other words, it doesn't occur most of the time.

Zz.

 

[PerennialII]

Yeah, our bearded guru opened one a while ago ...

https://www.physicsforums.com/showthread.php?t=101337

 

[Danger]

That's a beard? I thought that he was being assaulted by a wolverine.

By the way, how does one figure that hot water is in a denser state than cold water. That doesn't occur until after freezing when the crystal structure appears. (I think...)

 

[PerennialII]

That's a beard? I thought that he was being assaulted by a wolverine.
By the way, how does one figure that hot water is in a denser state than cold water. That doesn't occur until after freezing when the crystal structure appears. (I think...)

Somehow a doped koala comes to mind . Hot water ... degassing/less dissolved gas?

 

[Danger]

I suppose both of those are reasonable explanations.

 

[DaveC426913]

By the way, how does one figure that hot water is in a denser state than cold water. That doesn't occur until after freezing when the crystal structure appears. (I think...)

Volume decreases as temperature decreases, down to At 4C, then volume increases as temp. decreases to 0C. Thereafter, volume decreases.

 

[Danger]

Thanks, Dave. I never heard that before. What causes the reversal?

 

[DaveC426913]

As the temp drops, the molecules bounce around less, needing less room.
As the temp passes 4C and approaches 0C, the dipolar forces in the water molecules start lining up (this is, on a macro scale, freezing). Water molecules, when lined up, actually take up more room than if they are left to a disorganized jumble. So, as they start lining up, the volume begins to expand.
Once they are all lined up (frozen), they once again bounce around less and less, causing the volume to continue to shrink.

I just thought of an amazing analogy: a box full of coathangers*. When they're all jumbled up, you can compact them to a certain extent, but not below that. If you want to compact them even more, you'll have to pull them apart (expand) maybe even take some out of the box (i.e. burst a pipe) so that you can align them all in a more organized way, then, once they're organized (all lined up / frozen), you can now fit them back into a smaller space and continue to compact them.

*which I am now copyrighting (c) 2005 DaveC426913

 

[Danger]

Cool. Thanks.

 

[Mozart]

Why does ice's volume become greater than liquid water if its density increases?

 

[russ_watters]

Its density decreases - that's why it floats.

 

[Mozart]

Are there any other solids besides ice that become less dense then their other state(s)?

 

[DaveC426913]

Are there any other solids besides ice that become less dense then their other state(s)?

I'm not sure if there are.

Water is an incredible substance. It has loads of unique properties, many of which are critical to the existence of life as we know it. The ability for its solid to float on its liquid is just one.

 

[PerennialII]

... have been under the impression that it's quite unique ... someone will probably correct this . Behavior & properties of water and ice are one complex 'mix'. Even after all smart material, nano-"garble" etc. its weirdness still produces cool research topics (like material models of ice :!) ).