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Author Topic: Is Heat produced When Water Turns To Ice ?  (Read 12493 times)

Offline neilep

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Is Heat produced When Water Turns To Ice ?
« on: 04/01/2010 18:26:50 »
Dearest Ice-Ice-Baby-ologists !

What do ewe get when ewe cross a rainbow with an ice-machine ?

Ewe get this !




Kewl eh ?

Being delivered next Tuesday.



I'm a tad confused ! Ewe see..I thought when stuff happens..energy is made and released as heat yes ?...so...how come when water changes to ice it freezes ?...does this process not generate heat ? and thus, makes making ice an impossibility  ?

If I put some water in my freezer..where does the heat then go that the process of freezing generates ?


Hugs, shmishes, plugs, dishes



mwah mwah



Neil
Freeze A jolly Good Fellow
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Offline RD

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Is Heat produced When Water Turns To Ice ?
« Reply #1 on: 04/01/2010 19:18:13 »
Quote
The specific latent heat is the amount of energy required to convert 1 kg (or 1 lb) of a substance from solid to liquid (or vice-versa) without a change in the temperature of the surroundings -- all absorbed energy goes into the phase change -- is known as the specific latent heat of fusion.
http://en.wikipedia.org/wiki/Latent_heat#Specific_latent_heat

Need to add 334 KiloJoules of energy to change 1Kg ice at 0oC into 1Kg water at 0oC.
 

Offline Geezer

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Is Heat produced When Water Turns To Ice ?
« Reply #2 on: 04/01/2010 19:35:26 »
Ewe see..I thought when stuff happens..energy is made and released as heat yes ?...so...how come when water changes to ice it freezes ?...does this process not generate heat ?

As RD points out, it takes quite a lot of energy to convert ice into water. So, to convert water into ice, you have to remove energy, and you do this by removing the energy from the water in the form of heat. Your freezer is a lot colder than the water, so the water gives up its heat energy to the air in your freezer by warming up that air. Then the freezer tries to maintain its cold temperature by pumping the heat into your kitchen. So, if your kitchen gets too cold, you could make a lot of ice in your freezer to warm it up.
 

Offline neilep

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Is Heat produced When Water Turns To Ice ?
« Reply #3 on: 04/01/2010 20:14:09 »
woo !!

Thank ewe RD & Mr Geezer.

Kewl !!...so , remove the heat and ewe have ice !..when the actual water turns to ice..does that not itself just generate a little heat when it goes from liquid to solid ! ?
 

Offline Geezer

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Is Heat produced When Water Turns To Ice ?
« Reply #4 on: 04/01/2010 20:32:02 »
I dunno! I don't think it does.
 

Offline lightarrow

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Is Heat produced When Water Turns To Ice ?
« Reply #5 on: 04/01/2010 21:27:51 »
Kewl !!...so , remove the heat and ewe have ice !..when the actual water turns to ice..does that not itself just generate a little heat when it goes from liquid to solid ! ?
It should do it.
Suppose you have liquid water at -10°C (it's not a paradox, you can create it with specific expedients); it's in a non-equilibrium state and it can solidify suddenly(*). Then the latent heat of fusion have to be released and the ice have to become hotter, so the temperature goes, let's say, from -10°C to -5°C.

(*)as in these experiments:
http://www.break.com/usercontent/2007/8/super-cooling-experiment-350713
« Last Edit: 04/01/2010 21:43:48 by lightarrow »
 

Offline Geezer

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Is Heat produced When Water Turns To Ice ?
« Reply #6 on: 04/01/2010 22:35:11 »
Good idea! Supercooled water.
 

Offline Make it Lady

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Is Heat produced When Water Turns To Ice ?
« Reply #7 on: 05/01/2010 21:00:17 »
I remember in a science lesson heating up a block of ice in a beaker and plotting temp vs time. The temperature went slowly up but plateaued at the points where it turned from solid to liquid and liquid to gas. This was where the structure changed and hydrogen bonding broke down. I can remember being fascinated by this.
 

Offline Bored chemist

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Is Heat produced When Water Turns To Ice ?
« Reply #8 on: 06/01/2010 09:05:30 »
Kewl !!...so , remove the heat and ewe have ice !..when the actual water turns to ice..does that not itself just generate a little heat when it goes from liquid to solid ! ?
It should do it.
Suppose you have liquid water at -10°C (it's not a paradox, you can create it with specific expedients); it's in a non-equilibrium state and it can solidify suddenly(*). Then the latent heat of fusion have to be released and the ice have to become hotter, so the temperature goes, let's say, from -10°C to -5°C.

(*)as in these experiments:
http://www.break.com/usercontent/2007/8/super-cooling-experiment-350713

Just for the recotrd, once you get the supercooled water to freeze it is a mixture of ice and water so its temperature is exactly 0C.
The only way to avoid this would be to start with water so cold it would be a glass, then it could freeze and warm up to below freezing.

It's quite a counter-intuitive experiment to do. You can put a test tube of clean water in ice and salt  and cool it down slowly. It's rather surprising when the temperature suddenly rises when the water freezes.
 

Offline lightarrow

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Is Heat produced When Water Turns To Ice ?
« Reply #9 on: 06/01/2010 11:57:38 »
Just for the recotrd, once you get the supercooled water to freeze it is a mixture of ice and water so its temperature is exactly 0C.
Sorry but I don't understand the meaning of this phrase. If you have supercooled water it's not at 0°C or it won't be supercooled; if you mean that the temperature of the supercooled w. increases up to 0°C while it begins to freeze, that doesn't seems correct to me, since the freezing is fast and the system doesn't have time to reach the equilibrium. The temperature goes up to 0°C only after some time.
« Last Edit: 06/01/2010 11:59:13 by lightarrow »
 

Offline Bored chemist

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Is Heat produced When Water Turns To Ice ?
« Reply #10 on: 06/01/2010 12:29:52 »
The temperature won't rise to -5 C it will rise to exactly 0C when the stuff freezes.
 

Offline lightarrow

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Is Heat produced When Water Turns To Ice ?
« Reply #11 on: 06/01/2010 12:37:05 »
The temperature won't rise to -5 C it will rise to exactly 0C when the stuff freezes.
Do you mean immediately, while it's freezing? That's weird.
 

Offline Grey Area

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Is Heat produced When Water Turns To Ice ?
« Reply #12 on: 14/01/2010 21:08:01 »
Water and ice at exactly 0°C are in perfect equilibrium - it contains both water freezing to ice and ice melting to water in equal quantity. As soon as you move the temperature either way, you unbalance the equilibrium, producing either more ice (colder) or more water (warmer).
 

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Is Heat produced When Water Turns To Ice ?
« Reply #12 on: 14/01/2010 21:08:01 »

 

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