Seems like a dumb question but I've heard it and actually believed it could be true at least in some circumstances. Something about how hot water looses temperature faster and can end up getting below freezing faster.
Recently it came up in discussion with someone (a chemical engineer) and I was told how that simply couldn't be the case. I'm thinking I believed in an old wives tale.

No, that is impossible. First the hot water has to cool down to the cold water temp.

Wives tale.

Now what is not - perfectly still water (that where the surface tension is not broken) can be heated above 212 F and once tension is broken (disturbed) will immediately boil over.

Forgot what it's called but seen the experiment.

Seems like an easy experiment, if you had a 2 probe cooking thermometer you wouldn't even need to open the freezer to check.

I can't imagine it would be true though...

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Originally posted by c1steve:
No, that is impossible. First the hot water has to cool down to the cold water temp.

Thanks Steve, that's what she told me too. I guess I lost the bet!

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Originally posted by LS1 GTO:
Wives tale.

Now what is not - perfectly still water (that where the surface tension is not broken) can be heated above 212 F and once tension is broken (disturbed) will immediately boil over.

Forgot what it's called but seen the experiment.

Yes..... and one can boil water in a paper cup that is placed directly in a fire too.

Not so fast all you doubters. Ridewv, don't hand away your money yet.

I'm not going to post all the research, but Google the Mpemba effect, and prepare to be amazed...as well as confused.

It is an observed effect, but far from proven, or even explained science. Have fun with it.

Well, I'll tell you this. In our emergency generator room on the ship, there are hot and cold water lines running through the space and along the bulkhead which is adjacent to the outside deck. They run directly parallel to each other top and bottom.

Two winters ago--a brutally cold winter here on the Delaware--that space got extremely cold. The hot water line froze and burst the pipe. The cold water line never did freeze.

So make of that what you will.

yes, hot water freezes faster than cold water. in order for water to freeze the molecules have to give off their heat energy and arrange themselves in the certain way to freeze. molecules of hot water are moving faster, giving up their energy and helping them arrange themselves faster than cold water. The "theory" is called the Mpemba Effect .

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Originally posted by ridewv:

quote:

Originally posted by LS1 GTO:
Wives tale.

Now what is not - perfectly still water (that where the surface tension is not broken) can be heated above 212 F and once tension is broken (disturbed) will immediately boil over.

Forgot what it's called but seen the experiment.

Yes..... and one can boil water in a paper cup that is placed directly in a fire too.

Yup - I recall while in Cub Scouts my dad doing that for us. He built a fire in the middle of the front yard (small, but impressive due to house being in middle of city) and we all boiled water in our own cups.

Thanks Otto, I'm not conceding yet!

Baize' another factor could the differential in movement between the two lines. For instance if the cold line flowed more frequently say commodes flushing etc., whereas the hot line stayed stagnant longer. Right?

A quick brush through my college physics books brought me to the chapter on phase change, which explains that cold water will not freeze before hot water.

What it did say was that boiling water will freeze faster than hot water due to the energy given up through evaporation.

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can be heated above 212 F and once tension is broken (disturbed) will immediately boil over.

this is why you don't do the quick depressurize on your pressure cooker if you don't want it to boil.

quote:

Originally posted by Otto Pilot:
Not so fast all you doubters. Ridewv, don't hand away your money yet.

I'm not going to post all the research, but Google the Mpemba effect, and prepare to be amazed...as well as confused.

It is an observed effect, but far from proven, or even explained science. Have fun with it.

Yep, and a large component of contrail formation.

The rapidly expanding gases along with the water component in jet exhaust, result in the "dumping" of energy and the loss of molecular motion resulting in H2O freezing and the contrails form out of that process.

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Originally posted by ridewv:
Thanks Otto, I'm not conceding yet!

Baize' another factor could the differential in movement between the two lines. For instance if the cold line flowed more frequently say commodes flushing etc., whereas the hot line stayed stagnant longer. Right?

Not in this case. These two lines dead end after leaving this space. They go down to the deck below which is the machine shop sink. The hot and cold water gets used about equally at the sink. In fact, the hot water probably gets used a bit more.

Though before that space the lines do service two heads and a shower. So who knows.

I suppose one could test the theory by taking a pot of boiling water and a pot of room temperature water or water taken from the fridge and place them side by side outside this winter and watch which one freezes first.

quote:

Originally posted by LS1 GTO:
Wives tale.

Now what is not - perfectly still water (that where the surface tension is not broken) can be heated above 212 F and once tension is broken (disturbed) will immediately boil over.

Forgot what it's called but seen the experiment.

Thinking of "superheated"? When it finally goes it is commonly referred to as "bumping" in the sciences. While surface tension could have some effect, a more important factor is nucleation. Having a perfectly smooth clean flask is problematic- nowhere for microbubbles to start the boil. It eventually ends up over 100°C and spontaneous boiling results in violent release of hot liquid. Having a small scratch in the glass, or addition of an inert chip, can prevent.

What I have read of this previously, perhaps even here about ten years ago, is that most of water is insulated except the surface.

It is almost always the hot water pipes in a house that freeze, not the cold.

I actually ran this experiment once. Was not able to demonstrate the Mpemba effect; the cold water froze first. Note that this not disprove the Mpemba effect, it only means I was not able to reproduce it.

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Originally posted by Balzé Halzé:

I suppose one could test the theory by taking a pot of boiling water and a pot of room temperature water or water taken from the fridge and place them side by side outside this winter and watch which one freezes first.

I think surface area might play a factor in this experiment. Dump em both on your driveway.