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Author Topic: Which would reach room tempereature first ? Boilng or freezing water ?  (Read 8361 times)

Offline neilep

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Hi All,

My ear is still popping and driving me bonkers  by the way !!..I know ewe're all interested !!




Here is some rather hot water...careful now.....if you're a yoof make sure you have a grup (GrownUp) around before you get close!!






And here is an ice cube :...brrrrrr....careful...it's a cold one !!





Assuming the water is boiling at 100c and the ice cube is at 0c...and I moved them into my lounge which is about 21c.......which one would reach room temperature the quickest or slowest ?

Does hot water cool quicker than cold water gets warmer at room temperature ?


Y'see....I wish I knew !!..but I don't !!...perhaps ewe can tell me and WHY ?

Hugs and shmishes

neil

mwah mwah mwah mwah xxxxxxxx




« Last Edit: 13/11/2007 13:41:31 by neilep »


 

Offline Alandriel

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what altitude is your lounge at ?  ;D

I'm gonna ask now because I know that results will be different if you're doing your experiement at the Dead Sea or atop Mont Blanc
 

Offline neilep

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what altitude is your lounge at ?  ;D

I'm gonna ask now because I know that results will be different if you're doing your experiement at the Dead Sea or atop Mont Blanc

This is a good question and deserves merit...



* Sheepy checks ordnance survey map*.....ooops ...seems I'm in orbit !!..oh well..

.........lets humor me and assume the room is at sea level and the quantity of water is the same.... ;)
 

Offline lightarrow

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what altitude is your lounge at ?  ;D

I'm gonna ask now because I know that results will be different if you're doing your experiement at the Dead Sea or atop Mont Blanc

This is a good question and deserves merit...



* Sheepy checks ordnance survey map*.....ooops ...seems I'm in orbit !!..oh well..

.........lets humor me and assume the room is at sea level and the quantity of water is the same.... ;)
Where do you put the ice cube? In a glass? And the glass on a table? Then I presume hot water reaches 21C faster:

the ice cube require ~ 80 cal/g to melt; then liquid water, to go from 0C to 21C requires 21 cal/g; total heat: 101 cal/g.

hot water instead have to give away 100 - 21 = 79 cal/g to go from 100C to 21C.

Assuming the speed of heat flow is the same in the two opposite cases (from environment to ice in the first case; from hot water to environment in the second case), then the hot water cools faster than how ice melts and heat up.

Actually, the temperature difference between hot water and room temperature is higher than that between ice and room T, and this increase the speed of heat flow in the case of hot water, so this is a reason more of the faster cooling of hot water.
« Last Edit: 13/11/2007 17:00:22 by lightarrow »
 

Offline neilep

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See ?...I hope all you GUESTS are out there reading this.

This site is awesome !!...you ask a question....and then someone with the knowledge takes the time to respond.

All you guests should sign up now and make use of the valuable resources available here.

THANK YOU ALBERTO....
 

Offline Bored chemist

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The nearer the hot water gets to room temperature the smaller the difference in tmeperature between it and its surroundings.
Since it only loses heat because of that difference, as the temperature aproaches ambient the rate of change aproaches zero.
The hot water never reaches room temperature- it gets asymptoticly close.

The same goes for the melting ice.

Also, if you have a huge lump of ice and a small glass of hot water the outcome will be different from a huge kettle and a small ice cube.
 

Offline techmind

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The hot water never reaches room temperature- it gets asymptoticly close.
The same goes for the melting ice.

Yup. You could sensibly apply an arbitrary limit on closeness to room temperature at which point you'd declare the experiment over, e.g. ask "which gets to within half a degree celicius of room temperature the quickest?"
But in practice it will also depend how you're supporting the water/ice. Is the ice resting on a surface (plastic / thermally insulating, or metal / thermally conducting). Can the air flow freely around the ice? What sort of container is the water in (a thermos flask(!), glass bowl, metal tin)? Are there drafts in the room, or will the air circulate only by convection due to the temperature of the samples?
The more you look at it the more you can see that it's a poorly-defined question  ;D
 

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