Why does hot water freeze faster than cold?
 

Scientists offer £1,000 prize for answer to the question: Why does hot water freeze faster than cold?

• Ancient problem has eluded scientists and philosophers for centuries
• £1,000 reward offered to member of public who can provide 'convincing explanation' of phenonemon

By Daily Mail Reporter
PUBLISHED: 04:40 GMT, 27 June 2012 | UPDATED: 04:40 GMT, 27 June 2012




It is the baffling question which has perplexed the world's greatest scientific minds and even eluded great thinkers like Aristotle.
But now scientists have become so infuriated about the mystery of why hot water freezes faster than cold, that they have put up a cash reward to find the answer.
The Royal Society of Chemistry has offered £1,000 for a member of the public to come up with a convincing explanation for the phenomenon, which has mystified humankind.

http://i.dailymail.co.uk/i/pix/2012/...41_468x352.jpg Puzzler: The phenomenon of hot water freezing more quickly than cold has been dubbed the Mpemba Effect

The scientific problem, which has become known as the Mpemba effect, has also defeated Francis Bacon and René Descartes.

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The problem got its modern name in 1968, when Tanzanian student Erasto Mpemba posed the question to professors visiting his school.
http://i.dailymail.co.uk/i/pix/2012/...62_233x292.jpg The problem is so ancient its answer is said to have even eluded the great Greek philosopher Aristotle

Mr Mpemba, who had been studying the problem for five years, had asked Professor Denis Osborne, of Dar es Salaam University: 'If you take two similar containers with equal volumes of water, one at 35C and the other at 100C, and put them in a refrigerator, the one that started at 100C freezes first. Why?'
The professor was unable to answer and published a paper on the problem the following year, calling it the 'Mpemba Effect'.
Brian Emsley, media relations manager at the Royal Society of Chemistry, wrote in the Guardian that the winner of the £1,000 prize will need to 'make a convincing case and employ some creative thinking'.
Many standard physical effects are said to contribute to the phenomenon, although no single one has been conclusively proved as the cause.
Theories put forward based on evaporation, convection and supercooling have all been put forward, but as yet the question still remains unanswered.
Members of the public have until July 30 to submit their entries.
They will be pitted against worldwide postgraduate scientists, who, sponsored by the Royal Society of Chemistry, will be tackling the same problem.

Read more: http://www.dailymail.co.uk/sciencete...#ixzz1z1kW4xoO

My theory: Thermal inertia. Once it starts the accellerated shedding of heat, it's like a runaway train.

i was thinking that hot water expands allowing for space between the water molecules making it easier to freeze individual molecules as opposed to closer knit clusters of water molecules. thermal transfer does the rest. one drop of water (hot or cold) will freeze faster than a cup full, under uniform conditions...

does that make any sense?? lol

You're kidding right? Thermal inertia? LOL Heat has no mass. You must be an engineer!

I had always assumed that hot water froze before cold water because the former has a much lower concentration of dissolved gases. Cold water with it's dissolved nitrogen, oxygen and CO2, to name the main gases, behaves as a eutectic solution that exhibits a freezing point depression.

In college, I was the top student in Physical Chemistry - loved it.

I assume it's because the hot water triggers the thermo sensors in the refrigerator much sooner, triggering the compressor to come on right away, and run solid until it's frozen.

This wouldn't explain why hot water pipes always freeze first during a cold winter.

I understand what you mean... let me try to be more clear.
Sure, the heat energy ITSELF has no mass, but it does "transfer" to the colder air around the water. My theory is that when you have a larger amount of heat transferring, it sets up a "current" (kind of like electrical current) and it is that process of heat transfer that has the "inertia". Make sense?

Kind of an "intuitive" approach to the problem... quite often the WRONG way to think about scientific theories! http://www.discussworldissues.com/fo...ilies/grin.gif

Neat link on the problem.

http://www.neatorama.com/2008/08/22/...s-about-water/

my WAG....maybe because of the extreme temps between the two? and the difference in speed of molecular rotation?

Latent heat of vaporization adds additional cooling ... vaporization rate is greater for hot water

http://upload.wikimedia.org/wikipedi...2BWater%29.png

http://en.wikipedia.org/wiki/Enthalpy_of_vaporization

And the steam engine did more for the science of thermodynamics than thermodynamics ever did for the steam engine.

I can solve that problem, all it requires is a 1 Billion dollar grant from Washington, 20 years and a couple expeditions later I'll be able to give them an answer.

I tried this last winter, was way cold and no wind. Cold water froze first.

Water molecules hydrogen-bond to each other, forming complex structures within the water. The strength of these bonds are just below chemical bonds. Water at 35 C has already formed a lot of complex structures because it isn't being too disturbed. However, water at 100 C has almost no structures within it. As the water turns to ice, the structures within the water must be broken to form an ice crystal lattice. However, the hot water does not have any structure to it, so it easily arranges into an ice crystal lattice.

I probably has something to do with the fact that water is the only substance on earth that exists in three states naturally.

You're all wrong.....



...Its the jews.

Delta of nomenclature

All cooling systems remove heat, they don't add cold..

the cooling system will operate more efficiently/faster if it is hot.

God wanted water to be special.

It freezes faster when it is hot then cold and it gets less dense when it is colder rather then more dense like everything else.

Imagine how sinking ice would F up most temperate lakes.

http://en.wikipedia.org/wiki/Mpemba_effect

http://math.ucr.edu/home/baez/physic...hot_water.html

The UCR link has the nuanced answer.

To be honest I had never before heard (or thought) that hot water froze first. I think I will test it out myself today...

I used to play with that effect in high school. Take a glass of boiling water in sub freezing temperatures. Go outside and throw it up in the air, it will turn to snow before it hits the ground. I would only do it when it was below zero outside. But it works, kind of cool to watch.