Does hot water freeze before cold water

[Big Al 10]

if you want a scientific reply try here!!

 

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

 

Al

[Mo 10]

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.

[upholder 10]

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

[Big Al 10]

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

 

Al

[BARTMAN 10]

i think hot water freezes before cold

doesn't it have a special name

[Hal9001 11]

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

[Phanerothyme 12]

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.

[Lickszz 10]

Threads merged.

[Jamie 10]

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).

[Lickszz 10]

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

[MrH 11]

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

[Mo 10]

Originally posted by MrHelicopter

And if your windscreen cracks, send the bill to Mo

 

Fair cop