Why does hot water sometimes freeze faster than cold water?

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Re: Why does hot water sometimes freeze faster than cold water?

#41  Postby Rome Existed » Jul 01, 2012 2:20 am

Why did the physicist Rutherford win a Nobel Prize for Chemistry for his work in nuclear physics?
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Re: Why does hot water sometimes freeze faster than cold water?

#42  Postby Weaver » Jul 01, 2012 2:32 am

The Nobel Prize in Chemistry 1908 was awarded to Ernest Rutherford "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances".

http://www.nobelprize.org/nobel_prizes/ ... ates/1908/
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Re: Why does hot water sometimes freeze faster than cold water?

#43  Postby Rome Existed » Jul 01, 2012 2:37 am

Yeah, but he was doing it for physics!
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Re: Why does hot water sometimes freeze faster than cold water?

#44  Postby Weaver » Jul 01, 2012 2:40 am

I think the Committee really wanted to award two Nobel Prizes in Physics that year - so then came up with that BS line about chemistry to justify it.
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Re: Why does hot water sometimes freeze faster than cold water?

#45  Postby Rome Existed » Jul 01, 2012 2:42 am

In science, there is only physics, everything else is stamp collecting.



I bet he didn't appreciate getting a Nobel Prize in stupid Chemistry.
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Re: Why does hot water sometimes freeze faster than cold water?

#46  Postby Residue » Aug 16, 2012 7:02 pm

Me thought this was bog standard stuff, but maybe I'm too long outa the loop?

Basically it's a surface area exposure question, plus rates of exchange of energy between the two adjacent points in space.

1) The surface area question limits rates of exchange of energy ( only the hot exterior can lose heat quickly thus the inner core will be more insulated) unless some form of increased exposure between the two extremes can be maximised. Therefore if in hot material, it is fast cycling the hot interior to the exterior due currents within the material it will more rapidly expose its hottest parts to the coldest exterior, thus maximising rates of change to some extent. Rapid cycling within the material thus maximises surface area of hot material to cold - exposing the material constantly to greatest ranges of difference therefore greatest ranges of energy exchange.

2)The initial difference between the two temperatures seems directly proportional to the rates of cycling that can be self generated. Also the rate at which all pre set temperatures might converge upon zero could be plotted on a graph (A) to show at what point zero can be arrived at more quickly, both from the very low initial differences up to ranges that cool fast in spite of an increased initial temperature, due the effects of cycling.

We'll assume liquid at zero for these graphs.

Next we need a set of graphs to display the onset of freezing, from all the preliminary temperatures that converged upon zero, to take account of the latent heat of solidification. This might follow the same trend as in graphs (A), but may display some anomolies or displaced trends as compared to those already plotted.

The above could be repeated for identical samples containing various initial properties: deionised, various impurities etc that may enhance or reduce or introduce other aspects to the cycles of heat exchange.

Que sera.
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Re: Why does hot water sometimes freeze faster than cold water?

#47  Postby newolder » Nov 04, 2013 1:57 pm

Update from physorg: http://phys.org/news/2013-11-faster-cooler.html
Abstract
We demonstrate that the Mpemba paradox arises intrinsically from the release rate of energy initially stored in the covalent H-O part of the O:H-O bond in water albeit experimental conditions. Generally, heating raises the energy of a substance by lengthening and softening all bonds involved. However, the O:H nonbond in water follows actively the general rule of thermal expansion and drives the H-O covalent bond to relax oppositely in length and energy because of the inter-electron-electron pair coupling [J Phys Chem Lett 4, 2565 (2013); ibid 4, 3238 (2013)]. Heating stores energy into the H-O bond by shortening and stiffening it. Cooling the water as the source in a refrigerator as a drain, the H-O bond releases its energy at a rate that depends exponentially on the initially storage of energy, and therefore, Mpemba effect happens. This effect is formulated in terms of the relaxation time tau to represent all possible processes of energy loss. Consistency between predictions and measurements revealed that the tau drops exponentially intrinsically with the initial temperature of the water being cooled.

arxiv post
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Re: Why does hot water sometimes freeze faster than cold water?

#48  Postby Scar » Nov 04, 2013 2:56 pm

newolder wrote:Update from physorg: http://phys.org/news/2013-11-faster-cooler.html
Abstract
We demonstrate that the Mpemba paradox arises intrinsically from the release rate of energy initially stored in the covalent H-O part of the O:H-O bond in water albeit experimental conditions. Generally, heating raises the energy of a substance by lengthening and softening all bonds involved. However, the O:H nonbond in water follows actively the general rule of thermal expansion and drives the H-O covalent bond to relax oppositely in length and energy because of the inter-electron-electron pair coupling [J Phys Chem Lett 4, 2565 (2013); ibid 4, 3238 (2013)]. Heating stores energy into the H-O bond by shortening and stiffening it. Cooling the water as the source in a refrigerator as a drain, the H-O bond releases its energy at a rate that depends exponentially on the initially storage of energy, and therefore, Mpemba effect happens. This effect is formulated in terms of the relaxation time tau to represent all possible processes of energy loss. Consistency between predictions and measurements revealed that the tau drops exponentially intrinsically with the initial temperature of the water being cooled.

arxiv post


Can i haz the dummy version pretty plz?
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Re: Why does hot water sometimes freeze faster than cold water?

#49  Postby trubble76 » Nov 04, 2013 3:03 pm

Yeah, can you explain it for Scar please. Use short words where possible.

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Re: Why does hot water sometimes freeze faster than cold water?

#50  Postby newolder » Nov 04, 2013 3:07 pm

I don't think i could write it simpler than the linked article. :dunno:
... As everyone knows, water molecules have one oxygen atom and two hydrogen atoms—all held together by covalent bonds (the sharing of electrons). What's also known is that with water molecules, hydrogen atoms are also attracted to the oxygen atoms in other nearby water molecules—a force called a hydrogen bond. But, at the same time, the water molecules as a whole are repelled by one another. The team in Singapore has noted that the warmer water gets, the more distance there is between the water molecules due to the repellant force between them. That they say, forces the hydrogen bonds to become stretched out, and stretching out a bond means that there is energy being stored. That energy, the researchers suggest, is released as the water is cooled allowing the molecules to become closer to one another, and (as every chemistry student knows) giving up energy means cooling.

Warm water has more hydrogen bond stretching going on than cool water, thus it stores more energy, and has more to release when exposed to freezing temperatures. That is why, the researchers say, it freezes faster than cool water.


ETA Don't forget any rotational degrees of freedom: cool water (probably) stores its (heat) energy here rather than in the reported bond-stretching and the 'relaxation time' is (probably) longer for these. The (probably)s are due to me not being a chemist. ;)
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Re: AW: Why does hot water sometimes freeze faster than cold water?

#51  Postby Scar » Nov 05, 2013 7:17 am

newolder wrote:I don't think i could write it simpler than the linked article. :dunno:
... As everyone knows, water molecules have one oxygen atom and two hydrogen atoms—all held together by covalent bonds (the sharing of electrons). What's also known is that with water molecules, hydrogen atoms are also attracted to the oxygen atoms in other nearby water molecules—a force called a hydrogen bond. But, at the same time, the water molecules as a whole are repelled by one another. The team in Singapore has noted that the warmer water gets, the more distance there is between the water molecules due to the repellant force between them. That they say, forces the hydrogen bonds to become stretched out, and stretching out a bond means that there is energy being stored. That energy, the researchers suggest, is released as the water is cooled allowing the molecules to become closer to one another, and (as every chemistry student knows) giving up energy means cooling.

Warm water has more hydrogen bond stretching going on than cool water, thus it stores more energy, and has more to release when exposed to freezing temperatures. That is why, the researchers say, it freezes faster than cool water.


ETA Don't forget any rotational degrees of freedom: cool water (probably) stores its (heat) energy here rather than in the reported bond-stretching and the 'relaxation time' is (probably) longer for these. The (probably)s are due to me not being a chemist. ;)

I should have read the entire article, my bad. Thanks!
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Re: Why does hot water sometimes freeze faster than cold water?

#52  Postby Berthold » Nov 05, 2013 10:03 am

When the inside of the freezer is covered with a layer of frost, a warm container will readily melt through this layer, and the bottom of the container has direct contact with the freezer surface. A cold container will stay resting on the layer, which is a bad conductor of heat.

Are there any studies if the Mpemba effect works only under such conditions?
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Re: Why does hot water sometimes freeze faster than cold water?

#53  Postby jaydot » Dec 12, 2013 11:42 am

without knowing too much about the physics, i had an idea. if, when heated, molecules move further apart in a substance, maybe the cold air can invade the interstices more readily than into a cold substance. the cold is then not chilling the water, but the spaces in the water, resulting in hot water freezing more readily than cold.
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