Does cold water come to a boil faster the hot water?? (1 Viewer)

[Rod Melotte]

Does cold wather come to a boil faster the hot water??

Is this an urban myth that my daughter came up with? I debunked the Wizard of Oz Munchin hanging scene but can't find the truth in this one.

 

[Scott L]

I read in a science mag that hot water freezes faster than cold water so she may be right. Or maybe it's all another big April Fools joke?

 

[Greg_Y]

Cecil Adams addressed this in his Straight Dope column a few years ago. You can find his answer here:
http://www.straightdope.com/classics/a2_101c.html
Not as definitive as some of his posts, but alas, there it is.
He also tackled the issue of which freezes first:
http://www.straightdope.com/classics/a2_098b.html

 

[Shayne Lebrun]

Have you considered trying it?

'Twould make a fun experiment for you and the daughter, methinks.

 

[ken thompson]

The answer is no

 

[Vince Maskeeper]

Casting aside an constitutional difference between the two water samples (dissolved oxygen levels, other additives like salt)-- if we're talking about two "identical" samples of water...

Obviously the goal of boiling is to reach a certain temp plateau. Whichever starts closest to that plateau will have a decided advantage.

So, hot water will boil sooner, all things being equal.

-V

 

[Rob Longmore]

Water Boils at 100 Deg C, and freezes at 0 deg C this does not change.

 

[NickSo]

Why do they use hot water to re-ice skating rinks???

I hear its for a smoother skating surface... this true?

 

[ken thompson]

Because hot water does in fact freeze faster than cold. I forget why exactly. Perhaps because the molecules are more excited or perhaps the thin layer of steam on the hot water does something. Another thing about water that I found interesting is the fact that as water freezes it expands (hence it floats) but did you know that cooling water actually contracts until 4 degrees celcius then begins to expand?

 

[Todd Hochard]

Why do they use hot water to re-ice skating rinks???

I'm guessing here, but by putting down hot water, you'll melt an ever-so-small layer of the top ice, then that layer and the hot water refreeze together. This would tend to smooth out the imperfections on the top of the ice.

So, yes, I agree with you. It makes for smoother ice.

Oh, and I'm reaching here (dust out the cobwebs of my mind), but if I recall from my Nuclear Power days- it takes more energy to change water from liquid to gas phase, than it does to heat it from room temperature to just under boiling. Latent heat of vaporization.

Todd

 

[Todd Hochard]

Because hot water does in fact freeze faster than cold.

Another myth dispelled by straight dope above.

It would seem to me that such a myth would violate the laws of conservation of energy. After all, temperature is nothing more than a measure of the average kinetic energy of matter.

Todd

 

[ken thompson]

Myth? Look into it.

 

[ken thompson]

I'll find the explanation somewhere. I know it.

 

[Leo Hinze]

The great thing about this question is that it is not something that is open to personal interpretation. Physics of materials, a.k.a. Thermodynamics, has conveniently set out all the rules that answer this question.

And the answer to the question, does cold water come to a boil faster than hot water, is no.

 

[Vince Maskeeper]

Myth? Look into it.

I have. It doesn't.

-V

 

[ken thompson]

Well, then look here www.weburbia.com/physics/hot_water.html
The real answer is "it depends".

 

[nolesrule]

Water Boils at 100 Deg C, and freezes at 0 deg C this does not change.

Actually, it does change. The boiling and freezing points are a function of pressure and volume. That's why boiling point is lower at a high altitude where air pressure is lower.

 

[Vince Maskeeper]

Wait. This question is about boiling water. The Mpemba effect is specifically about freezing water.

In fact, the reason behind the Mpemba effect (gasses in hotter water escape allowing easier manipulation of temp) would also point to hotter water boiling faster.

The original question is about boiling water, and the answer is no that hot water will boil faster.

-V

 

[ken thompson]

Yes that was the original question but this thread had changed direction before my comment about freezing hot water to which You and Todd scoffed. I was simply defending my position.

 

[Jay Taylor]

The old wives tale that hot water freezes faster than cold was very prevalent in the past. Perhaps that is due to the type of freezers that were used before frost-free freezers were invented.

Most home refrigerators in the 1950’s had to be defrosted periodically. They had metal freezer compartments instead of plastic. About an inch of frost would build up in the freezer section before many people would get around to defrosting their refrigerator. Combine that with the clumsy metal ice cube trays that most people used and you can see what would happen.

Putting boiling water in a metal ice cube tray then placing it on a layer of frost would cause it to melt the frost, sink down to make contact with the metal freezer housing and then provide better cooling of the water than a tray filled with cold water that didn’t melt the frost.

Today we try this with our plastic ice cube trays and frost-free refrigerators with plastic freezer compartments and we think our ancestors were mistaken. But with 50's era trays and freezers perhaps they weren't.

This idea was briefly mentioned in the link Ken Thompson provided above. Read the 4th condition for the Mpemba effect, which is “Surroundings”.

Jay Taylor