Why does hot water freeze faster ?

[ledhed]

Help me out here..it seems hot water freezes faster than a like amount of cold water.. can someone explain this ?????

 

[Red Eye Racer]

HMMMMMM,..... does cold water boil faster than warm water?


Im gonna pull a theory directly outta my rectum and see how close I am.


The warm water molecules are moving faster and spread further appart, therefore they are more exposed to the cold,.. so, in essence the cold can get to the molecules faster than if they started cold.

 

[Attila_Da_Hun]

Originally posted by ledhed
Help me out here..it seems hot water freezes faster than a like amount of cold water.. can someone explain this ?????

It doesn't. Trust me.

 

[Der Alta]

The best explanation I could find: (credit www.newscientist.com/lastword)

it is possible to produce ice cubes more quickly by using initially hot water instead of cold. The effect can be achieved when the container holding the water is placed on a surface of frost or ice. The higher temperature slightly melts the icy surface on which the container rests, greatly improving the thermal contact between the container and the cold surface. The increased rate of heat transfer from the container and contents more than offsets the greater amount of heat that has to be removed. The effect cannot be obtained if the container is suspended or rests on a dry surface.

This effect was first noted by Sir Francis Bacon using wooden pails on ice. My own investigation showed ice cubes could be obtained within 15 minutes rather than 20 minutes if the frost in the refrigerator was deep enough. The incentive to get your ice a little quicker is obviously greater in Australia than in cooler countries.

AO

 

[ledhed]

you just spawned a hemmoroid ! Hehe..I'm cheating research gives me a headache ..I was hoping someone new the correct answer

 

[Der Alta]

Ahem....

AO

 

[Jugend]

uuu?? I don't get it at all ledhed.

It's like saying "If you smoke 2 paks of red marlboros a day in 2 weeks you'll be able to run a marathon faster than before"

How have you come up with this? If it is any true in this then it's pretty cool.

RER:s explanation probably has some true in it, because the molecules moving should make 90 C water drop to 80 faster than 20 C to 10. But it should have to do with both the molecule movement speed and that the temperature difference to the cooling source is much greater for the hot water. (unless you cool the 90 C water with a 0 C source and the 20 C water with a -70 source.)

[EDIT] Der Alta, thanks for clearing this up!👍

 

[Duke]

I didn't read Alex's article, but hot water does not freeze faster than cold water. You need to remove X amount of heat before water freezes, X being the difference between the water temperature and 32 degF (O degC). The bigger the difference, the longer it takes to freeze at a given rate.

What it does is freeze more clearly. This is because the air bubbles have more time to perc out of the freezing water. So for crystal clear ice cubes, fill your trays with warm water.

 

[Der Alta]

More fuel to the fire:
http://physics.hallym.ac.kr/education/faq/hot_water.html

AO

 

[duo17]

Originally posted by neon_duke
I didn't read Alex's article, but hot water does not freeze faster than cold water. You need to remove X amount of heat before water freezes, X being the difference between the water temperature and 32 degF (O degC). The bigger the difference, the longer it takes to freeze at a given rate.

What it does is freeze more clearly. This is because the air bubbles have more time to perc out of the freezing water. So for crystal clear ice cubes, fill your trays with warm water.

I always thought the white looking area in the middle is from a mineral build up, not air bubbles (although those are there too).

 

[Red Eye Racer]

Originally posted by duo17
I always thought the white looking area in the middle is from a mineral build up, not air bubbles (although those are there too).

yep,........... air.

 

[Klostrophobic]

http://www.straightdope.com/classics/a2_098b.html

The Straight Dope rules.

 

[SS69]

i always thought it was the sudden change in temperature.

 

[oosacker]

Did you know that you can freeze water by heating it? I leaned that in physics some time.

 

[hanker]

Originally posted by oosacker
Did you know that you can freeze water by heating it? I leaned that in physics some time.

Maybe that explains why when i was younger and i went for a bath, the water felt soo hot, it actually felt cold, that or my mom was trying to kill me

 

[ledhed]

Thanx for the help the links were great.