Posted on 06/27/2012 12:41:32 AM PDT by neverdem
It seems a simple enough question - yet it has baffled the best brains for at least 2,300 years.
Now the Royal Society of Chemistry is offering £1000 to the person or team producing the best and most creative explanation of the phenomenon, known today as The Mpemba Effect.
Competition judges will be looking for an outside-the-box, inventive submission. In addition, the format of the submission should be creative and eye-catching.
Any medium or technology can be employed to make the case, including articles, illustrations or even film.
Submissions can be based on, and reference, existing research. The winning submission will be scientifically sound, and arresting in presentation and delivery.
The public has four weeks to crack the case before a group of the world's brightest young science brains take on the challenge in London as one aspect of a special science communications meeting entitled Hermes 2012.
Fittingly, that group's bid for glory will be made in the first week of the Olympics. The sharpest international postgraduate science students will travel to England from around the globe to participate in the Hermes 2012 event.
The Royal Society of Chemistry is sponsoring this visit to the UK of the hand-picked young scientists, who will gather at Cumberland Lodge in Windsor Great Park...
(Excerpt) Read more at rsc.org ...
The specific gravity of water goes down until 39 or 40 F, 4 C. Then it goes slightly up until 32F or 0C where it stabilizes.
Thank you.
Same reason a boat floats: the ice has a greater volume than liquid water, so it's less dense than the same volume of water. An object that is less dense than the water it displaces is forced upward, i.e., is bouyant. Young engineers at Old Dominion University are given first-hand experience in this effect in their annual Concrete Canoe contest.
What that whole essay seems to be saying is that the hot water freezing faster is an illusion, caused by other factors which act upon the water.
Apparently, quite a few things need to be controlled in order to test the hypothesis that hot water freezes faster. The water must be degassed (to control for the change in freezing point caused by solutes). The water must be prevented from evaporating, which causes other complications—hot water can only be prevented from evaporating by putting it in a container that does not expand, and preventing it from expanding increases the pressure, and increasing the pressure increases the freezing point. So the cold water would have to be subjected to the same pressure. The water must be cooled slowly, so as to avoid the supercooling effect. And the water should be stirred to maintain an even temperature—but the stirring will lower the freezing point—although this may not be necessary if the cooling is sufficiently slow to prevent supercooling.
I remember doing crystallization studies back in undergrad chemistry classes. We had to put crystals into a tiny glass tube, and put the tube into a heater that took forever to heat. Then we sat there, looking through a magnifier at the crystal until it started to melt, and record the temperature. As I recall, the temperature change had to be very slow to get an accurate reading.
I also recall from those chemistry classes that a pure substance has to spend some time at a particular internal temperature before it undergoes a phase change. That is because the substance must gain or lose internal kinetic energy (depending on the direction of the phase change) before it can undergo the transition. Once the energy is gained or lost, the phase change occurs fairly rapidly.
Okay. 'series'. I was gonna say what you did neverdem, but in a simpler way.
Kinda like hot water molecules = car going 100 mph and hitting a concrete wall, vs a car going 10 mph and hitting the wall. The 'wall being Ice' in the case of water. And mph = molecular 'speed'.
I haven't had to use that stuff since I learned it around 1975. Then forgot it as soon as I could thanks to those personal computer thingys and MS programs from that nasty and evil Bill Gates guy.
"But by the 20th century the phenomenon was only known as common folklore, until it was reintroduced to the scientific community in 1969 by Mpemba, a Tanzanian high school pupil. "
Something about this rings false to me. In 1965, a high school teacher of mine challenged me to do this same experiment at home, in private conversation with him. Later on that week or maybe a month later, he extended that same challenge to others in my class. So, somehow it was not "reintroduced to the scientific community" by someone who lived in Africa, but was apparently widely known in America.
By the way, no one who did the experiment found that hot water froze more quickly. The teacher laughingly explained that it success was more an effect of poor housekeeping -- that hot water melted ice/frost in the freezer, allowing the container more intimate contact with the freezer coils.
Look at your line going to your icemaker in your frige——bet it is hooked up to your house hot water line. lol
My guess would be that it involves the amount of adsorbed gasses in cold water as opposed to hot water.
Heating the water over an extended period drives the adsorbed gasses out. So cold water will have more gasses adsorbed in it.
Adsorbing a gas in water lowers the freezing point. We’ve all seen this with a can of coke that’s very cold but still liquid, and when you pop-the-top and let some co2 out it immediately freezes.
I once heard on a science radio show that evaporation (aka, less mass to freeze) is the key to the story.
Warm water makes for less cloudy ice cubes.
“Warm water makes for less cloudy ice cubes.”
I didn’t know that, but probably the same reason... less devolved gasses. You could test this by putting the cold water in an ultrasonic cleaner first. This will drive the gasses out.
Because if that we not true, life on this planet would probably not have been possible. The fact that ice floats is incredibly important. I've always found it fascinating that water is one of only a couple of known substances that are less dense as solids than they are as liquids.
That's pretty much what I thought as well, mainly because of the clarity of the ice you get with hot water, as opposed to cold, although I think the speed of freezing also has something to do with how cloudy ice is.
Stand back folks! I'm going to attempt ... science!
Whoever he was.
Hint: It’s related to the fact that water takes longer to boil if you stand there and watch it.
RSBC offers £1000 for explanation of an unsolved legendary phenomenon
Royal Society of Body Chemistry ^ | 26 June 2012 | NA
Posted on Wednesday, June 27, 2012 3:41:32 AM by neverdoneit
Why does a hot woman warm up faster than a frigid woman?
Note to self: When doing technical writing at 3 AM, expect to make glaring mistakes.
The layman’s version of wideminded’s answer: Because H20 in it’s solid form forms hexagonal crystals. Any lattice structure is always going have more surface area for the same mass as a non-latticed structure. What made you think this was unknown?
Sometimes, some places, it gets cold enough to freeze water even without refrigeration. Besides, you can make ice in cool temperatures that are way above freezing. The Romans did it in antiquity.
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