Why Does Hot Water Freeze Faster Than Cold?

[EatUrShorts]

Hi my name is Bruno, I'm 19, I'm currently finishing my 12nd grade on arts.

I'm annoyed because no one I know can properly discuss the Mpemba effect with me.

So, I'll go as fast as I can on this.

The scenario.

We have a cup of water let's say for example at 80 degrees Celsius .
We have another cup of water let's say for example at 20 degrees Celsius.

And then we have a for example freezer, with a room temperature of let's say -40 degrees Celsius.

You put both cups in the freezer at the same time and done voila, the cup that was at 80 degrees Celsius freezes faster than the one that was at 20 degrees Celsius.

Now why? Nobody knowns.

What I think?

Kinetic energy.

The water has different stages , and those stages have different molecular behavor and kinetic energy.

Now at 0 or under degrees there is no kinetic energy, there are only crystals, over 0 degrees and below 100 the molecules are stable altough they start moving a bit more as the temperature rises, over 100 they just go ballistics nearly breaking their molecular links

So we have the cup with water at 80 degrees, it comes in contact with a colder environment and they react, causing a temperature shock, which creates more kinetic energy, causing the 80 degree water molecules to go nuts and almost break their links, (even making some of the water to go from liquid to gas) thus making it easier to cool than the 20 degrees celsius that goes down gradualy because the molecules are stable.

I tought of this theory based on behaviour I saw on video of a vulcano. Where the ash cloud coming from the vent reacted with the cold air creating a mini thunderstorm.

I have no more patience to keep writing xD I hope you read this and take a quick look, I already think I'm wrong since, I don't know if this theory is actually possible in a such small scale .

See you. Hugs and good night.

 

[Drakkith]

So we have the cup with water at 80 degrees, it comes in contact with a colder environment and they react, causing a temperature shock, which creates more kinetic energy, causing the 80 degree water molecules to go nuts and almost break their links, (even making some of the water to go from liquid to gas) thus making it easier to cool than the 20 degrees celsius that goes down gradualy because the molecules are stable.

I don't know what a "temperature shock" is. But I can tell you that it most certainly does not 'create' more kinetic energy. I see no reason why hot water coming into contact with cold air would cause the water molecules to suddenly start breaking their bonds. It should have the opposite effect.

Now, I have heard of warm water freezing faster than cold water before, and I've seen a few threads on it here on PF. If you do a search you should find some that have possible answers.

I tought of this theory based on behaviour I saw on video of a vulcano. Where the ash cloud coming from the vent reacted with the cold air creating a mini thunderstorm.

Yes, but you have to ask yourself, "What does this have to do with how fast cold and hot water freeze". Of which the answer is, "Nothing". The two effects are completely different.

 

[Vanadium 50]

There are already at least 32 threads on this subject. You can find out a lot by using the Search box.

 

[EatUrShorts]

Thank you for awnsering :3 I'm sorry I'm new to the forum, I just wanted to share my quick vision xD
Yeah not temperature shock - Thermal shock xD sorry I'm portuguese I don't know the therms in english. You musn't forget the glass cup! I said almost breaking, not breaking :P which makes it easier for the water to cool, because it's less dense , we can't ignore the fact that cold water is denser than hot water and ice. and yes the its opposite effect, but it doesn't happen right away, some molecules that are going nuts escape, thus creating gas which has more kinetic energy than the previous form.

 

[mrspeedybob]

Here's a well written paper that discusses the possible causes...

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

 

[EatUrShorts]

Thank you! :3

 

[russ_watters]

Have you tried to replicate the effect? I have, and it didn't happen. One of those threads has details of my test...

 

[EatUrShorts]

Could you link it please russ? Well I've been reading some experiences and it could have to do with impurity on the water it self, or the actual fridge. And the material you use to put the water on has to have some kind of influence for sure, where did you put the water? If you have like a cup of glass or a cup of metal or something that heats with the water, it has that initial thermal shock which helps out a lot the process. Plastic for example isn't as good.

 

[russ_watters]

Here: https://www.physicsforums.com/showthread.php?t=205920
Post #17, bottom of the first page. There is an additional graph posted on the second page. Some other members posted links to scholarly papers on the issue.

 

[EatUrShorts]

Hum ty :3 One small thingh tough... Shouldn't you have done it one at a time? Or get a fridge for each. Because by putting all of them together it kind of takes away the point since you're altering the temperature of the fridge...

 

[russ_watters]

The cups of water are pretty small compared to the capacity of the fridge, plus if the logic is that you are raising the temp of the fridge it will have a bigger adverse effect on the cooler water anyway.

In any case, I hadn't heard of that as a constraint of the setup and you are more than welcome to try such a test.