Science Question....
Being the grunt that I am, and only having taken one semester of college, therefore having not reached the level of education warranting the taking of thermo-dynamics, I have a question.
We have a big chest freezer in our building. Since it is insufferably hot in this country, the entire freezer is dedicated to water bottles, with exception of the Otter Pops my wife sends me. We take frozen water bottles out on patrol with us so we have cold water throughout our patrol. Anyhoo...
I was checking to see if I needed to add more bottles. The freezer was moderately full. I picked up a bottle of water that looked clear to check the temperature. It was cold. When I squeezed it, it immediately went from liquid to the consistency of a 7-11 Icee, spreading from the middle towards both ends. I picked up another and banged it against the side of the freezer bottom first. Same result, the water turned to slush, spreading upwards from the point of impact.
Can anyone tell me what causes this phenomenon? I would think that the excitement of the molecules would create friction between the agitated molecules, causing heat (a negligible amount)?? But the water becomes slush. Is it becoming colder due to the agitation?? How does this happen??
Any answers, please leave them in the comments.
SCOUTS OUT!!!
MDG....OUT.
posted by Michael @ 8:31 AM
14 Comments:
Can't give you an answer, but I can just picture you picking up every bottle to make sure they all do it. I miss watching your inquisitive mind work. You are so cute - I love you!
What you had was a super saturated ice/water solution.
A certain amount of heat needs to be removed from water for ice to form. In your solution, there was too much ice for it to remain soluble, so when you banged it, the turbulence caused the ice to fall out of solution.
You can also do this with your microwave somtimes. You can put a cup of water in the microwave for long enough to boil it. You look in the oven, and the water isn't boiling. You open the door, and touch the cup, and all the sudden the water starts to boil.
You can do a similar thing with supersaturated salt solutions. You heat water to just under boiling, and add salt until you it isn't going into solution anymore. Add just enough water to get the excess salt into solution. Let the solution cool. Once the solution has cooled to room temperature, drop a single grain of salt into the solution. All of the excess salt will fall out of solution, almost instantaneously.
Neat, isn't it?
Oh, and Good Hunting!
MDG,
Dude, I have an MA and I couldn't figure that out either. I'd stop by the Army gym in Kirkuk and grab a bottle out of the freezer to watch the water turn into slush. I was like a moth to the flame.
It's the small things in life.
Owen...Thanks for the answer. It makes total sense. That's cool.
El Capitan- Me too. My wife was right, I did it to every bottle in the freezer, just cause it was cool to watch.
I think it's crystallization -- it was JUST at the freezing point, and your movement started the ice crystallizing.
I can get the geek squad to weigh in on the matter; I know you don't believe there's a geek bigger than me, but I've got a whole crew of 'em at my disposal! ;)
MDG:
I have an MS in chemistry -- don;t know if you want this eactly right, but Owen is essentially right save the use of the term "super saturated." That terms referes to dissolving salt or other things in water or other solvent. Rather what you have is a lack of "centers of nucleation." There is no way I can explain that fully in comment, takes diagrams and math, but the idea Owen conveys is right, just thought I'd correct the vocabulary.
Right, John! Like you can get superheated water in the microwave when you heat in a very smooth container because there aren't nucleation sites for the bubbles... then when you tap it, all of a sudden you've got a rolling boil...
I guess that's what I was getting at, kinda. :)
Oh darn, I was too late to give the explanation. Yes, the center of nucleation is the right answer. If you watch ice cubes freeze, they start at the edge (where there may be a rough spot for the crystal formation to start) and then it builds upon itself. I did the same thing with the Sprudle (do you remember "sprudle"??? effervescent mineral water) bottles in Germany. (Sorry, MGD, you were very young, probably too young at the time to remember). The case of bottles would be delivered to our door in Germany. They were so cold, the moment I picked them up, the crystal formation would slowly spread from top to bottom. I remember the fascination I had when I saw this happen. Just like your wife, I believe, too, that you did it to every bottle to see it happen over and over again. Glad you have ways for keepin' cool. LUV YA!
Incredible! The power of the web of connections here before my very eyes....can you imagine how long it would take to get this question answered by three knowlegable people when posed at a backyard BBQ?
Well, I guess if you lived near Los Alamos or Oakridge National Labs and your neighbors were all those kinda people...but that's not my neighborrhood!
Labrat gibbie...
Actually, you've got it wrong, water is a fairly unique chemical in that its freezing point increases as pressure is applied. Hence ice skates work because they concentrate pressure under the narrow blade... the water melts and then provides a film of water for the skate blade to glide upon.
When the water in the bottles is supercooled, especially if it is several degrees below the normal freezing point, almost any tiny disturbance will be enough to initiate nucleation.
And once freezing starts, another phenomenon that you probably didn't notice... the actual temperature of the water/ice mixture in the bottle rose to 32F. The ratio of ice that forms to water remaining is directly related to the amount of supercooling that takes place prior to the actual commencement of freezing.
The same principle is used in certain little reusable heat-packs. They contain a highly concentrated solution of sodium acetate, which will completely dissolve at a moderately high temperature (I forget just what it is... probably around 125F). If the mixture is quite free of impurities and any particles, it can be cooled to quite low temperatures before it will crystalize on its own. The bags have a little metal clicker-disk built in, and when you click it, the solution is disrupted sufficiently to begin nucleation and crystalization. And when it crystalizes, the solution returns to its natural crystalization/freezing point. And it keeps giving off heat until crystalization is complete. And they are reusable many, many times, being regenerated by just tossing the little pouch into some boiling water for a bit.
Hope this helped
DRK
"... the water melts and then provides a film of water for the skate blade to glide upon"
DaveK-- does this explain too why waxing skis helps them on snow? That would answer a question I've had for a long time.... Thanks.
A good link to supercooling is wikipedia http://en.wikipedia.org/wiki/Supercooling
Very broadly speaking, molecules in liquid water under 0C don't know to which direction they should start linking to form ice crystals.
Waxing skis... another matter altogether, I think.
As best I know, the main purpose of waxing your skis is to prevent the snow from sticking to the skis. Although there is some localized melting of ice crystals due to pressure from the skis, because the pressure is so broadly distributed, there isn't really much melting that occurs. But the wax does provide a slick surface for the ski to glide over the flattened snow (or other surfaces as well... for example, skiing down sand-dunes). Which wax is best will depend somewhat on the temperature of the snow.
And for cross-country skis (the old, traditional ones, without the little "fish-scale" bottoms) it's even more complicated... you have to strike a balance between the ski being able to grip the ice crystals while the ski is at "rest" and still being able to glide while the ski is in motion. With different amounts of pressure on different parts of the ski, often more than one kind of wax must be used. And when the temperature of the snow changes, you'll probably have to stop and completely rewax. Truly an art to get it right.
DRK
At first I thought my wife had touched it. I swear she's got ice in her veins. Kind of like Lilith Frasers wife on that TV show Cheers.
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