The Vespiary

The Hive => Chemistry Discourse => Topic started by: GOD on July 18, 2002, 11:15:00 PM

Title: Hot vs Cold water (freezing)
Post by: GOD on July 18, 2002, 11:15:00 PM
why does an equal volume of hot water freeze faster than cold water?  Swim guesses that its because there are fewer molecules.  His little nephew schooled him on that one... :(  ::)

EDIT:
sorry, swim was under the impression that although it was a very simple question, that it was related to general chemistry..?..
Should he post all of his dumb-assed newbie questions there?(the couch) -regardless, thanks for the link...appreciated.
i FEEL funny.
Title: couch topic
Post by: hypo on July 18, 2002, 11:33:00 PM

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

Title: Mpemba Effect
Post by: carboxyl on July 18, 2002, 11:40:00 PM
Yes hot water freezes faster than cold water in many cases. The hot water does loss mass due to evaporation. Water cooling from boiling to freezing (100C to OC) can lose anywhere from 10%-18% of it's total mass.

Another interesting reason is because of the density of water. Water is most dense at 4C as we all know. If you have water which is already cold at 4C, the water on top which is exposed will freeze first, for all practical purposes, ie, not submerged in liquid nitrogen etc. since the water on top freezes, it becomes less dense than the rest of the water, which remains insulated under the thin layer of ice on top. But this is different when freezing hot water. As the top, exposed layer of hot water cools, it becomes more dense than the rest of the water. It then falls to the bottom, cooling instead of insulating, and causing more hot water to rise to the top to be cooled. This convection process deals with cooling the water to 4C rapidly.

Cold water also contains more dissolved gasses than hot water. These dissolved gasses lower the freezing point of water.
The above post is purely fictional. Any resemblance to "real-life" is purely coincidental.
Title: Momentum
Post by: Flip on July 19, 2002, 12:08:00 AM
Certain reactions function with a certain type of momentum.  I was always under the impression that this occured as 95*C water will lose it's heat exponentially faster in a freezer than 50*C water as the degrees are further apart.  The more extreme the temperature is to one side or another, the faster it transfers heat/cold to opposing conditions. Of course the 95*C water will eventually become 50*C water... but I think the molecules maintain a certain momentum with heat transfer that reduces the temperature more quickly.  That is one theory I was told but I don't remember anyone saying for sure.

Flip
Title: I've heard this before and never believed it.
Post by: Osmium on July 19, 2002, 10:59:00 AM
I've heard this before and never believed it. This is some weird shit.
I'm not fat just horizontally disproportionate.
Title: Just put 2 plastic jars in freezer.
Post by: raffike on July 19, 2002, 11:19:00 AM
Just put 2 plastic jars in freezer.Both with 200 ml water.Jar 1 water temp=38C.Jar 2 water temp=21C.Let's see which one freezes first.
A friend with speed is a friend indeed
Title: Yeah, swim didnt believe it at first either, he ...
Post by: GOD on July 19, 2002, 09:54:00 PM
Yeah, swim didnt believe it at first either, he ended up shelling out $10 to his little nephew after he tried it...
i FEEL funny.
Title: Maybe the cold water becomes temporarily ...
Post by: endo1 on July 20, 2002, 07:52:00 AM
Maybe the cold water becomes temporarily supercooled (temp < 0 without freezing). Perhaps someone doing this test should check the temp of the cold water when the "hot water" freezes? If this is the case then could this be applied to purification of safrole or other substance via feezing by heating up the sas oil (or other) before placing it in the fridge or freezer?
Title: Maybe the cold water becomes temporarily ...
Post by: carboxyl on July 20, 2002, 12:10:00 PM
Maybe the cold water becomes temporarily supercooled (temp < 0 without freezing). Perhaps someone doing this test should check the temp of the cold water when the "hot water" freezes?If this is the case then could this be applied to purification of safrole or other substance via feezing by heating up the sas oil (or other) before placing it in the fridge or freezer?

The water does become supercooled. the water begins crystalizaion at under 0C, but the temperature stablizes. water's weird. These tests have been done. What benefit does this have for freezing sassy? Quicker seperation times? I like to take my time when freezing for monster crystals 8)

EDIT RE TESTS DONE: I found this site in which Thomas A. Jennings Ph.D claims to have performed thousands of such tests.

I must have witnessed the freezing of thousands of samples of water and never once - no not once - did I ever witness ice forming at 0C.


http://www.phase-technologies.com/html/vol._5_no._5.html (http://www.phase-technologies.com/html/vol._5_no._5.html)

   


The above post is purely fictional. Any resemblance to "real-life" is purely coincidental.
Title: It's because when water is heatd the molecules ...
Post by: humidbeing on July 20, 2002, 02:48:00 PM
It's because when water is heatd the molecules are in
faster motion and the attractive elements are more easily
aligned so that a crystal lattice forms faster.
This is why (i think) that you can have a glass full of sass
cold as hell, and than knock it,  and it will freeze all
at once. I think this is the mechanics of nonnewtonian
fluids, that occurs with certain substances at lower
Temps. Meaning that some stuff becomes like non newtonian
 liquids at lower temps.
CG I miss you sweety, I really do.
Title: > It's because when water is heatd the ...
Post by: Osmium on July 22, 2002, 11:35:00 AM
> It's because when water is heatd the molecules are in
> faster motion and the attractive elements are more easily
> aligned so that a crystal lattice forms faster.

That doesn't make any sense. The water only freezes when it is cold, so the molecules will have slowed down by then.

I'm not fat just horizontally disproportionate.