Can hot water freeze faster than cold water?

[Fluff]

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

[Brian Ellis]

I have never conducted such an experiment, but I can say that tap water which has been heated to ~60°C and cooled will freeze faster than tap water that has never been heated. I have observed this in two similar copper pipes that ran through a barn: one was a hot water and the other cold tap water. At night, if there was a frost, of a certain intensity, the hot water froze and the cold water didn't. I observed this on at least a dozen occasions and never the opposite. I never researched why but mentally hypothesised that it was the loss of dissolved salts by heating the fairly hard water.

[Umfriend]

The next question is: can cold water boil faster than warm water.

[Brian Ellis]

Originally posted by Umfriend
The next question is: can cold water boil faster than warm water.

If you put it in a vacuum, yes!

[High_Jumbllama]

I remember from a chemistry class in high school that water that should be a gas or solid can stay in liquid form if pure and motionless enough. I've seen containers of water freeze all the way through in under a second after the've been below freezing for minutes and heated water in a microwave can suddenly vaporize with pressure changes due to opening the door. Either something precipitating out of the water or localized differences in pressure can give the state change a location to start from which very quickly spreads through the whole volume.

[VJ]

Yes, an example is supercooled water. It is quite common in the atmosphere and dangerous for aviation: as soon as it hits the plane, it turns to ice. (IIRC, it cannot occur at temperatures below -40°C)

As for superheated water: this has caused accidents when heating water in the microwave (it doesn't seem to be boiling, but when you move the glass, it suddenly does behave like boiling water).


Jörg

[ZokesPro]

Wa...ter...


Is this some sort of non-alcoholic beverage or liquid?

[gt40]

Originally posted by ZokesPro
Wa...ter...


Is this some sort of non-alcoholic beverage or liquid?

Yes, but bland as it is, it may be deemed palatable with the addition of hops and yeast.

[ZokesPro]

You mean.... BEER!!!

[Paddy]

I'm not physics buff!

I think hot water will freeze faster than cold water.. I always assumed that it was down to the large difference between the water temp and ambient causing a massive temperature drop. However Brian's theory about the loss of dissolved salts sounds much more plausible!

I have a heated discussion with my mate about superheated water. I'm sure we've all done it. -heat water in a microwave then add coffee with a spoon *don't try this at home kids!

I told him that I had seen water exist at temperatures greater than 100'C. I assumed that was because 100'C was the 'average' boiling point of water at STP, but my mate disagreed and said that all water evaporates at 100'C. I think we settled on superheated water not actually being water, but water with small pockets of steam inside. The steam doesn't evaporate due to the lack of nucleation points in the glass.

Anyway, I'll ask him .....

[Brian R.]

Most any physical phenomenon can happen under the correct circumstances, even if it is not thermodynamically favorable. The statement that is not investigated is: Can warmer water ever freeze before cold water when kept at equilibrium with their environment. The answer is probably "no". Nor can water be supercooled or superheated under those conditions

[ZokesPro]

When you microwave water it will reach a temp of 104C until... until something or rather, but I know that superheating water using microwaves, the water will go above 100C.

[Brian R.]

Don't forget that the author of this article is using the word "water" very loosely. Water is only one thing. If you add impurities to it, you are no longer talking about water, but about a solution or suspension of a solute in water. Then, all bets are off.

[Paddy]

Indeed....

But as I said, I'm no physics buff

[Elie]

You are correct!!!

Tap water for example contains many elements such as chlorine, salt, and various other particles which all effect boiling and cooling tempratures.

Note: the best water to test with is distilled water because it is the purist.

From my understanding about heating water in microwaves is this...
A microwave heats an element from the inside out, we know the surface of the water is like a vary thin layer (let's call it glass), this is why belly flops aren't a good idea

Anyway, this glass layer is not being broken keeping the temperature of the water higher than the natural boiling temperature of water.
After you superheat water and break that thin glassy layer, all hell breaks loose because the temperature underneath that surface is super hot, an awesome explosion will occur.

I'm not a physics guru either but it only makes sense

Regards,
Elie

Originally posted by Brian R.
Don't forget that the author of this article is using the word "water" very loosely. Water is only one thing. If you add impurities to it, you are no longer talking about water, but about a solution or suspension of a solute in water. Then, all bets are off.