I've been having a discussion with a friend and I'd like peoples thoughts/answers on the following:

If 2 buckets of water are placed in a location where the ambient temperature is the same (enough to freeze water) which bucket will freeze first, a bucket of cold water or a bucket of warm water?


My friend believes that the bucket of warm water will freeze first. This is because there is a greater heat loss from the warm water and so the temperature falls quicker, thereby freezing quicker.

I on the other hand believe the bucket of cold water will freeze first because the warm water may cool quicker at first but will then after a couple of minutes follow the same cooling curve thereafter. The cold water will still have been cooling also so would freeze first. I am not sure if this would vary if the size of water containers was bigger or smaller. What do you think?

I think you're right.

The size would only make a difference if the two containers were differnt sizes. Otherwise, it wouldn't matter whether they were ice cube makers or wheelie-bins.

It's after 10 at night and you're posing physics problems. Thanks a bunch.

fwiw, imho, the cold one would freeze first, or they would freeze together. If the warm one does cool more quickly then, at some point, it would attain the same temp as the other and they would then cool at the same rate together.

Why don't you test this theory yourself by placing a cup of cold water in your freezer along with a warm cup of water and see which freezes first.

Ill go for the cold.

So your friend is saying the hotter the faster something cools? Hmmm... So a semi frozen bucket of water would freeze after a bucket of near boiling water?

Dosent sound right to me.

The cold water will freeze faster than warm water.

However, it is possible for boiling hot water to freeze faster than hot water.

Why?

Water gives off steam therefore the amount of water to freeze would be less and therefore it cool and freezes faster.

I'm not sure what tempatures are require to make this condition work - probably higher than boiling point.

a luke warm cup of water will freeze faster (and cleaner) than a room temperature cup of water ;)

Originally posted by scaramanga
Ill go for the cold.

So your friend is saying the hotter the faster something cools? Hmmm... So a semi frozen bucket of water would freeze after a bucket of near boiling water?

Dosent sound right to me.

Not semi frozen. Just cold water and warm water. My friend agrees that with small volumes of water, as in an icecube tray, the cold water will freeze first. However, their reasoning with a much larger volume, as in the case of a typical bucket. As the warm (I emphasise WARM, probably around 100F or 38C) water cools in contact with the air and the inner surface of the bucket, it tends to sink towards the bottom, being denser. This results in convection currents, downwards near the inner surface of the bucket, and upwards in the centre. These currents continue, although slowing down as the water cools, resulting in a more efficient transfer of heat through the bucket, and from the surface of the water, to the colder air.

My friend claims this has been demonstrated by experiment, with the observation that the originally warm water freezes from the sides and base of the bucket inwards. The cold water, on the other hand, freezes initially on its surface, as water at 4C (maximum density) will have slowly sunk to the bottom of the bucket, and water at < 4C rises to the top.

My friend is a Science teacher, so who am I to argue?

Originally posted by The Cycleracer
Why don't you test this theory yourself by placing a cup of cold water in your freezer along with a warm cup of water and see which freezes first.

I have already tried it. Here is my reasonings and findings why I am convinced the cold water would freeze first.

I agree that it is true that the hot sample will initially lose heat at a faster rate than the cool sample, which can offset the obvious fact that it has to become cool before it freezes, but in the case of buckets full of water, this would only happen in a near vacuum. The hot water could only possibly freeze first in more normal circumstances IMO when the ambient temperature is much lower than either sample and the samples have a high surface area: volume ratio. For example, an ordinary ice-cube tray filled with cold tap water froze solid in my freezer compartment in less than a fifth of the time taken for the same tray filled with recently boiled water to freeze. (I opened the door every minute to check progress, which obviously tainted the results, but I suggest a time difference of 500% is fairly conclusive). When the tray was only half filled, the time difference was about 400%, a quarter filled, 100%. When I just barely covered the bottom of the tray with water, in both cases the sample had frozen the first time I checked.

From my results, I conclude by extrapolation that a bucket full of hot water, having a much lower surface: volume ratio than an ice cube tray, would have taken many many times longer to freeze than a bucket of cold. I cannot claim direct proof of this hypothesis since my bucket won't fit in my freezer compartment.

The warm water will freeze first, strange as it may seem.

The temperature to which you do this experiment does make a different

Scientific American (http://www.sciam.com/askexpert_question.cfm?articleID=0008EB6B-6C7E-1C71-9EB7809EC588F2D7)

Alaska Science Forum
March 5, 1984

Does Hot Water Freeze Faster Than Cold?
Article #650

by Larry Gedney

This article is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Larry Gedney is a seismologist at the Institute.

Every year, there are some questions repeated by readers regarding the same subject. The most common of these has been: would a glass of hot water or a glass of cold water freeze first, if left outside in subzero temperatures?

Although the issue has been discussed before in this column, the interest generated merits repetition of the subject.

Almost any scientist would scoff at the question and state that it is frivolous--I did myself. Obviously, so the reasoning goes, the glass of hot water has many more calories of heat to dispose of before it can become frozen, and therefore must take the longer time to freeze.

"Not So!" say the proponents of the other side. "How come my hot water pipes always freeze up before my cold water pipes?" And "How come when I put out glasses of hot and cold water when it's - 40°F, the hot water freezes first?"

I never put much credence into these claims until I started reading different accounts of the phenomenon. Most recently, the distinguished scientist and author, Isaac Asimov, in his Book of Facts (Red Dembner Enterprises Corp., 1981), flatly states in one of his "3000 facts," that "Water freezes faster if it is cooled rapidly from a relatively warm temperature than if it is cooled at the same rate from a lower temperature."

This may be true, but only under certain circumstance. Dr. T. Neil Davis (editor of this column from 1976 to 1981) performed his own experiments, and found that only when he used Styrofoam cups at temperatures near zero, did warm water freeze first.

Under almost any other circumstance, especially those which allowed heat to escape through the sides of the container, such as from a metal cup, the colder water froze first.

Insulation being taken into account, we can now attribute the hot water freezing first to the fact that, in hot water, circulation currents move faster, exposing more water to the air, and resultant evaporation (hence, cooling) occurs at a greater rate. Also, boiling the water before exposure to frigid temperatures removes the dissolved air which inhibits freezing in the colder water.

The stubbornness sometimes exhibited by scientists in accepting observations of laymen in favor of accepted scientific dogma sometimes leads to such comments such as those appearing in a recent Ann Landers column. An expert scientist was consulted and asked to reply on this same question--could warm water sometimes freeze before cold, given the same conditions. He said absolutely not. I would have said the same thing.

We were both wrong.

if you want a scientific reply try here!!

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

Al :)

Next time your windscreen is frozen over pour cold water over one part to clear it and slightly tepid water on the other part and see which side refreezes quickest. It is always the warmer side that freezes fastest.

It's the unique properties of water like this that made life possible on Earth.
I think it's the only liquid that freezes from the top downwards.
If it froze from the bottom upwards there would have been no life in the oceans during the frozen periods of the Earths history.
I'm no expert, just one of the things that I remember from school 8)

If I remember my physics correctly, H2O is the only liquid that freezes from the top down. IE the ice floats

Al :)

i think hot water freezes before cold
doesn't it have a special name

Does Hot Water Freeze Faster Than Cold?
This question, first raised in 1969 by a Tanzanian student named Erasto Mpemba is still a topic for controversy today. When a container of water is placed in a freezer, there are many factors which can affect the length of time it will take to freeze, and under the proper combination of circumstances, a given volume of hot water in a container may freeze faster than the same volume of cold water.
Some factors which can contribute to this phenomenon are:


Evaporation:
Hot water is more likely to evaporate from a container than cold water, leaving a reduced volume of water in the container. Less water takes less time to freeze. Also, the evaporating water it pulls heat from the water remaining in the container, reducing its temperature and thus its freezing time.

Conduction:
When a container of hot water is placed on an icy surface in a freezer, the hot container will melt the ice on the surface. The melted freezer ice will provide better thermal contact with the hot container, allowing better conduction of heat from the hot container than from the cold container placed in the same environment.

Convection:
Water is most dense at 4C. When a container of uniformly cold water freezes, it generally forms a skin of ice, which is less dense, on the surface. This skin insulates the remaining volume of water, impeding heat loss. In the container of hot water, as the surface water cools to 4C, it is more dense than the hot water below, and sinks, forcing more hot water to the surface to be cooled. This sets up convection currents which can cause the container of hot water to lose heat more rapidly than the container of cold water.

Impurities:
Water usually contains impurities such as dissolved gases, dust particles, etc. These impurities can lower the freezing temperature of the water, and also provide nucleation points which cause ice crystals to form. Some of these impurities are driven out when water is heated. The purer hot water may actually have a higher freezing temperature than the cold water, and it may also be subject to supercooling. When this occurs, the entire volume of water remains liquid below its freezing point, then the entire volume freezes solid rapidly. The cold water may tend to form ice crystals on the impurities, insulating the remaining water in the container, and there may ultimately be some liquid water in the container when the formerly hot container has frozen solid.
It is important to remember that in an experiment such as this, a great many factors come into play, many of them quite subtle, and initial conditions are crucial in determining the outcome.



Source (http://www.noblenet.org/reference/hotcold.htm)

how cold is cold?

how hot is hot?

If I put two identical ceramic mugs in the freezer, one with an inch of water at cold tap temp (about 10 degc) and one with an inch of water straight of the boiling kettle(about 90 deg c) - the cold water freezes first in the freezer compartment of a household upright fridge freezer


Believe me, I've tried it when faced with precisely this question.

Of course the true answer is - it depends, not least on the exact temperatures of the two bodies of water, the temperature of the freezer, the nature of the containers used, they type of freezer used, the type of water used etc. etc.

Threads merged.

Originally posted by Lickszz
If 2 buckets of water are placed in a location where the ambient temperature is the same (enough to freeze water) which bucket will freeze first, a bucket of cold water or a bucket of warm water?

Neither will freeze !! (but the water inside the buckets might freeze).

Thanks for stating agreed FACTS your opinion on the case is missing. ;)

Originally posted by Mo
Next time your windscreen is frozen over pour cold water over one part to clear it and slightly tepid water on the other part and see which side refreezes quickest. It is always the warmer side that freezes fastest.

And if your windscreen cracks, send the bill to Mo :D

Originally posted by MrHelicopter
And if your windscreen cracks, send the bill to Mo :D

Fair cop :D

Why should anyone care?

hey people I've been searching high and low to find the answer to the question " does hot water freeze before cold water." Almost every website that I've been to says "yes" so why are people so split on this? it would be nice if someone could give me one solid answer

hey people I've been searching high and low to find the answer to the question " does hot water freeze before cold water." Almost every website that I've been to says "yes" so why are people so split on this? it would be nice if someone could give me one solid answer

Why dont you try experimenting? :huh:

Surely you'd find out :confused:

Yes - it might be nice to have an answer in time for this threads 5th birthday! :hihi:

hey people I've been searching high and low to find the answer to the question " does hot water freeze before cold water." Almost every website that I've been to says "yes" so why are people so split on this? it would be nice if someone could give me one solid answer

That's the point, it seems to depend.

There are so many factors involved that the question really needs to be much more specifically stated to have one precise answer.

The warm water will freeze first, strange as it may seem.

what ^ says ;)

I dont know why but I was told if I was to use water on my windscreen to clear the ice, to not use hot water because it will freeze quicker, so in your answer I would go for hot water freezes quicker than cold water.

How many people are going to remember this and try it when the weather changes lol?

Cold water will always freeze the sooner.
It is basic laws of thermostatics that it has to.
I have however seen silly things of boiling water being thrown in the air, and the steam freezing into snow.
But that is not the same thing is it?

If you use water, no matter what temperature on your windcsreen, it will freeze, if the temperature is beloww what is known as the 'triple point'.
This is the point at which water can exist in all it three points.
Your windscreen call be clear completely, and then next moment be blocked completely by ice.
It is only really when you have the car completely warm that you are safe from this.
I sometimes have a completely clear car, then turn into the east wind, only to find my windscreen completely iced again, totally agianst the rising sun.
And that aint no fun, I can tell you.

Get anti freeze for your windscreen and then at least you will live.

Cold water will always freeze the sooner.
It is basic laws of thermostatics that it has to.

Except in those cases when it doesn't; due to the boiled water having less impurities in it, or evaporation having reduced the amount of water in the hot container, and various other factors mentioned above, some seven years ago.

Jeez ... I was gonna have a go at this thread, then realised it was eight years old! Has SF now got so boring that we have to dredge back so far ... it seems to be going on a lot recently.
Hot water freezes much quicker than cold water, just to be on topic :loopy:

Alaska Science Forum
March 5, 1984

Does Hot Water Freeze Faster Than Cold?
Article #650

by Larry Gedney

This article is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Larry Gedney is a seismologist at the Institute.

Every year, there are some questions repeated by readers regarding the same subject. The most common of these has been: would a glass of hot water or a glass of cold water freeze first, if left outside in subzero temperatures?

Although the issue has been discussed before in this column, the interest generated merits repetition of the subject.

Almost any scientist would scoff at the question and state that it is frivolous--I did myself. Obviously, so the reasoning goes, the glass of hot water has many more calories of heat to dispose of before it can become frozen, and therefore must take the longer time to freeze.

"Not So!" say the proponents of the other side. "How come my hot water pipes always freeze up before my cold water pipes?" And "How come when I put out glasses of hot and cold water when it's - 40°F, the hot water freezes first?"

I never put much credence into these claims until I started reading different accounts of the phenomenon. Most recently, the distinguished scientist and author, Isaac Asimov, in his Book of Facts (Red Dembner Enterprises Corp., 1981), flatly states in one of his "3000 facts," that "Water freezes faster if it is cooled rapidly from a relatively warm temperature than if it is cooled at the same rate from a lower temperature."

This may be true, but only under certain circumstance. Dr. T. Neil Davis (editor of this column from 1976 to 1981) performed his own experiments, and found that only when he used Styrofoam cups at temperatures near zero, did warm water freeze first.

Under almost any other circumstance, especially those which allowed heat to escape through the sides of the container, such as from a metal cup, the colder water froze first.

Insulation being taken into account, we can now attribute the hot water freezing first to the fact that, in hot water, circulation currents move faster, exposing more water to the air, and resultant evaporation (hence, cooling) occurs at a greater rate. Also, boiling the water before exposure to frigid temperatures removes the dissolved air which inhibits freezing in the colder water.

The stubbornness sometimes exhibited by scientists in accepting observations of laymen in favor of accepted scientific dogma sometimes leads to such comments such as those appearing in a recent Ann Landers column. An expert scientist was consulted and asked to reply on this same question--could warm water sometimes freeze before cold, given the same conditions. He said absolutely not. I would have said the same thing.

We were both wrong.


I'll requote that since it was several years ago when it was posted.

I'll requote that since it was several years ago when it was posted.

Because it was long winded, and tries to be funny, dosent make it any more of a load of ******** than it is now.
Stop believing in old wives tales.

Because it was long winded, and tries to be funny, dosent make it any more of a load of ******** than it is now.
Stop believing in old wives tales.

Ok how about university of California Physics dept: http://www.desy.de/user/projects/Physics/General/hot_water.html

Ok how about university of California Physics dept: http://www.desy.de/user/projects/Physics/General/hot_water.html

I dont care what it says, I am not even going to read it.
It is nonsense, the laws are the laws..

http://www.youtube.com/watch?v=HhuzjkE65f8

I dont care what it says, I am not even going to read it.
It is nonsense, the laws are the laws..

You're quite something aren't you - actively seeking to remain ignorant.

I dont care what it says, I am not even going to read it.
It is nonsense, the laws are the laws..

http://www.youtube.com/watch?v=HhuzjkE65f8

Being wrong doesn't bother you? Well, being wrong when you have the chance to educate yourself, nothing wrong with being wrong if you don't know any better.

Being wrong doesn't bother you? Well, being wrong when you have the chance to educate yourself, nothing wrong with being wrong if you don't know any better.

Latent heat is latent heat, it will never alter.
To freeze water you need to remove that latent heat.
You also need to remove its sensible heat, this varies with temperature.
The higher the temperature, the greater the heat.

If you can remove both those, with one above the other, you have created a heat engine with above 100% efficiency.
Which is impossible.
Stop wasting your time.

Balpin - the University of California know better than you.

Warm water can and does freeze more rapidly than warm water undercertain conditions.
You choosing not to believe and being pompous enough not to bother to read up and educate yourself doesn't change the reality.

Doubtless you'll puff and bluster, but how sad. People would have more respect for you if you read the information and conceded that were wrong.

Balpin - the University of California know better than you.

Warm water can and does freeze more rapidly than warm water undercertain conditions.
You choosing not to believe and being pompous enough not to bother to read up and educate yourself doesn't change the reality.

Doubtless you'll puff and bluster, but how sad. People would have more respect for you if you read the information and conceded that were wrong.

If that is the case then we are god.
We can create something from nothing.
Absolute and utter tosh.

Balpin - the University of California know better than you.

Warm water can and does freeze more rapidly than warm water undercertain conditions.
You choosing not to believe and being pompous enough not to bother to read up and educate yourself doesn't change the reality.

Doubtless you'll puff and bluster, but how sad. People would have more respect for you if you read the information and conceded that were wrong.

:)
Should say cold but we know what you mean. Which freezes first depends on the volume of water, start temperatures and the container.

Latent heat is latent heat, it will never alter.
To freeze water you need to remove that latent heat.
You also need to remove its sensible heat, this varies with temperature.
The higher the temperature, the greater the heat.

Nobody is disputing that. Your error is in failing to recognise that there's more than one way of removing latent heat.

Under the right conditions, hot water will evaporate into the air at such a rate, and remove with it such a large amount of latent heat, that there is actually less of it left in order to freeze that water, than there is in the water that was cool to begin with.

You are correct in insisting that to turn a given volume of hot water into ice, will always take longer than to turn the same amount of cold water into ice. You're failing to see that because of evaporation, the hot water ends up as partly ice and partly water vapour.

Nobody is disputing that. Your error is in failing to recognise that there's more than one way of removing latent heat.

Under the right conditions, hot water will evaporate into the air at such a rate, and remove with it such a large amount of latent heat, that there is actually less of it left in order to freeze that water, than there is in the water that was cool to begin with.

You are correct in insisting that to turn a given volume of hot water into ice, will always take longer than to turn the same amount of cold water into ice. You're failing to see that because of evaporation, the hot water ends up as partly ice and partly water vapour.

Yes, so therefore I am correct.
Then given ammount of water always freezes as it shoud.
You are talking about crystalisation I think, which is snow, not ice.

Nobody is disputing that. Your error is in failing to recognise that there's more than one way of removing latent heat.

Under the right conditions, hot water will evaporate into the air at such a rate, and remove with it such a large amount of latent heat, that there is actually less of it left in order to freeze that water, than there is in the water that was cool to begin with.

You are correct in insisting that to turn a given volume of hot water into ice, will always take longer than to turn the same amount of cold water into ice. You're failing to see that because of evaporation, the hot water ends up as partly ice and partly water vapour.

It’s to do with the fact that ice forms quickly on the surface of cold water, the ice insulated the water below and slows down the freezing.
In warmer water ice freezes from the sides, heat can continue to escape up through the service so freezes sold more quickly.
But it does depend on start temperature, volume and container.

Yes, so therefore I am correct.

Insofar as you insist on talking about equal volumes of water yes.

Nevertheless, it is possible to place a cup of hot water and a cup of cold water into the freezer and for the hot water to freeze first.

Insofar as you insist on talking about equal volumes of water yes.

Nevertheless, it is possible to place a cup of hot water and a cup of cold water into the freezer and for the hot water to freeze first.

Technically it would be equal volumes of ice because you would have to start with unequal amounts of water.

Technically it would be equal volumes of ice because you would have to start with unequal amounts of water.

I'm not enough of a physicist to express myself, perhaps.

It will always take longer to convert one kilogram of hot water into one kilogram of ice, than to convert one kilogram of cold water into one kilogram of ice. (The volume will of course change.)

If you place two one-kilogram vessels of water in the freezer, the hot one may sometimes freeze first, but you would end up with less than a kilogram of ice in it.

I'm not enough of a physicist to express myself, perhaps.

It will always take longer to convert one kilogram of hot water into one kilogram of ice, than to convert one kilogram of cold water into one kilogram of ice. (The volume will of course change.)

If you place two one-kilogram vessels of water in the freezer, the hot one may sometimes freeze first, but you would end up with less than a kilogram of ice in it.
I don't think that’s the case either, it’s a lot more complicated than how much evaporation takes place and the effect can take place in a closed container so no evaporation. What I do now is that science hasn’t fully answered the question why it can freeze faster.

what ^ says
.. a few years ago; maybe it's changed in the interim!