Why does hot water freeze faster?

[sarah_444]

Cold water won by the way, don't ask me how or why though. At least now I have ice.

[Delovely5150]

So what happens to people when they're bored? They make Delovely laugh! *Marks check on her list and moves on to the next*

[Lysippos]

Okay to put this to rest.

The Mpemba effect isn't always observed, sometimes it is and sometimes it isn't. That is why scientists puzzle over this.

My guess would be that it has something to do with dissolved gas.

[aztek]

it doesn't.

anyone tried it????

i did.

it has to be a bit warmer than cold sample.

i have tried it few times, same cups with same amount of water, WARMER water freezes faster, not hot water.

in my experements, i used cold water from faucet, and same amount of the same water that has been sitting in the room for few hours, and was at room temp. NOT HOT.

don't believe me? try it yourself.

[StevenM Arizona]

The longer that water remains at a constant temperature, the more hydrogen bonds and water clusters are subsequently formed between the water molecules. Water at a near boiling temperature has highly excited molecules, which effectively prevents the formation of clusters and intermolecular hydrogen bonding. Thus, to create the organized lattice structure of ice, hot water has fewer clusters and hydrogen bonds to break than does cooler water.

A useful real life analogy in visualizing the organization of liquid water molecules into a solid lattice is what I call the lifeboat model. Consider hot water to be represented by active people on a cruise ship, walking all decks randomly throughout the ship. Cool water, with its water clusters and hydrogen bonding, is represented by meal time where some of the guests are seated in an organized fashion at their tables, while others are at various parts of the ship.

If a command was given to immediately fill all of the lifeboats (form ice), the model in which the dining guests are organized and contained in one location would theoretically take longer to disassemble their structure and rearrange into the boats than the model in which the guests are already moving about randomly, unencumbered by any given structure.

Thus, the reason that hot water freezes more quickly than cooler water is that hot water, with its excited molecules, has fewer hydrogen bonds and corresponding clusters than cooler, more organized water.

[lightly]

Because it's less dense. .. how do i collect the thousand pds ?

I'm just guessing... but... ?¿?

[Immunetoplacebo]

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

Nothing about the fridge being responsible for the effect. I'd speculate that it's caused by the hot water drastically increasing the air-moisture within the fridge, or at least the air-temperature if done with closed containers (which in turn allow for more moisture). And that that drastically increase heat conduction speeds since water is much better at it than (dry) air.

Normally there is very little moisture in freezers since any moisture form ice crystals. However it should only start forming ice crystals again in large quantities after the hot water has frozen.

Edited August 8, 2012 by Immunetoplacebo

[JesseCuster]

A useful real life analogy in visualizing the organization of liquid water molecules into a solid lattice is what I call the lifeboat model. Consider hot water to be represented by active people on a cruise ship, walking all decks randomly throughout the ship. Cool water, with its water clusters and hydrogen bonding, is represented by meal time where some of the guests are seated in an organized fashion at their tables, while others are at various parts of the ship.

If a command was given to immediately fill all of the lifeboats (form ice), the model in which the dining guests are organized and contained in one location would theoretically take longer to disassemble their structure and rearrange into the boats than the model in which the guests are already moving about randomly, unencumbered by any given structure.

Thus, the reason that hot water freezes more quickly than cooler water is that hot water, with its excited molecules, has fewer hydrogen bonds and corresponding clusters than cooler, more organized water.

In order to make the analogy closer you'd have the dining guests beside the life boats and the randomly walking around guests on the top deck as cold water has less distance to travel so to speak than the hot water to reach freezing point. It's not so obvious then that the guests on the top deck would fill the lifeboats faster as even though they can get moving faster, they have a lot longer to walk to reach the lifeboats.

Anyway, as far as I know, the Mpembe effect is very rarely observed and is not a general principle that hot water takes less time to freeze than cold water. I think it takes some special circumstances in order for it to work.

[CRIPTIC CHAMELEON]

Ahhhh is this one of those trick questions like what came first the chicken or the egg, ? I'll go with boiled.

[Super-Fly]

LOL.

Try chucking boiling water on you windscreen in the winter.

Makes a pretty mess.

Thanks,

[B Randomly]

Activity of molecules, along with thermal inertia.

Crude ananlogy: If a person is running naked through the tundra, they will die quicker than a person who stays at rest, to conserve their core temperature/energy.

it takes longer for the lack of heat to affect the room temp water because it is in a relaxed state. The boiling water is already in an excited state, so it is more likely to be influenced by an external source, or in this case, lack of external source. Once the energy starts to deplete, the depletion is set into motion and the doubling factor takes over.. -1°, -2°, -4°, -8°, -16°. The room temp water is affected much later than the boiling water because boiling stops as soon as you remove it from heat(starting the temperature drop "inertia")...

Make sense to anyone?

[Immunetoplacebo]

Can someone post the criteria for the effect? Are the containers air-tight and do they have to be put in an enclosed space (freezer) for it to work? I assume you have to test one at a time and wait for the freezer to fully cool down before testing the new one.

[JesseCuster]

Activity of molecules, along with thermal inertia.

Crude ananlogy: If a person is running naked through the tundra, they will die quicker than a person who stays at rest, to conserve their core temperature/energy.

it takes longer for the lack of heat to affect the room temp water because it is in a relaxed state. The boiling water is already in an excited state, so it is more likely to be influenced by an external source, or in this case, lack of external source. Once the energy starts to deplete, the depletion is set into motion and the doubling factor takes over.. -1°, -2°, -4°, -8°, -16°. The room temp water is affected much later than the boiling water because boiling stops as soon as you remove it from heat(starting the temperature drop "inertia")...

Make sense to anyone?

No, because the rate at which something cools is proportional to the temperature of its surroundings.

Hot water will start to drop in temperature rapidly because the temperature difference between it and the freezer is very high. But as the temperature of the water drops, the rate at which it cools gets slower and slower so that when it reaches a lower temperature it cools at the same rate as water that was put into the freezer originally at that temperature. This is how things work under normal circumstances. The Mpemba effect is an exception to the general rule.

It's like arguing that dropping something from a higher height will cause it to hit the ground sooner because it will build up more speed. It'll hit the ground at a faster speed, but it'll take longer than if dropped from lower down because it has further to travel. Similarly, hot water will start off cooling faster than cold water, but the rate of cooling will slow down so that when it becomes cold water it loses heat at the same rate as water which was

Think about it this way - hot water has to become cold water on its way to freezing. But if cold water takes longer than hot water to freeze, then the remaining time for the now cold water to freeze is longer than the time taken for hot water to freeze which is entirely illogical.

The problem y'all are having is that you are assuming the Mpemba effect is always true. You can do this experiment yourself by putting hot and cold water in the freezer and the cold water will indeed freezer much faster. It's only under specific conditions that aren't well understood that the exception works and the hot water freezes faster.

Edited August 12, 2012 by Archimedes