Another explanation for the Mpemba effect

[Charmonium]

The Mpemba effect is the idea that hot water freezes faster than cold water. WHAAAA!?!? What witchcraft is this you say. And many scientists would agree. But many would also disagree. It seems that either proving or disproving the effect has been a notoriously difficult thing to do. But so has explaining it if it is in fact real.

In a paper published online December 6 in Journal of Chemical Theory and Computation, scientists propose that hydrogen bonds, the links formed between hydrogen atoms and the oxygen atoms of neighboring water molecules, could be part of the puzzle. Dieter Cremer of Southern Methodist University in Dallas and colleagues studied the strengths of hydrogen bonds in simulations of clusters of water molecules. “We see that hydrogen bonds change when warming up water,” says Cremer. The strength of hydrogen bonds depends on the arrangements of nearby water molecules. In simulations of cold water, both weak and strong hydrogen bonds were observed, but in higher temperature simulations, a larger percentage of the hydrogen bonds were strong, because “the weaker ones are broken to a large extent,” Cremer says.


Cremer and colleagues realized their new understanding of hydrogen bonds could explain the Mpemba effect. As water is heated, weaker bonds break, and groups of molecules form into fragments that can realign to form the crystalline structure of ice, serving as a starting point for the freezing process. For cold water to rearrange in this way, weak hydrogen bonds first have to be broken.

https://www.sciencenews.org/article/debate-heats-over-claims-hot-water-sometimes-freezes-faster-cold

 

[NoTine42]

I once did a science project testing how long it took to freeze a tray of ice cubes starting with cold water vs hot water.... and the tray of hot water froze faster.

 

[darkswordsman17]

Learning that there really has not been a clear proof either way was one of those "everything they taught me in school was a lie" moments. I remember teachers basically just saying that hot water freezes faster and that was it, no real explanation (now that I think of it, it actually often seemed to be used as a way of dismissing not explaining other stuff as it was supposed to be one of those "it doesn't make sense, but this is how it works!" type of things; sometimes they'd come up with a plausible but under real scrutiny nonsense explanations). And then finding out that was hardly concretely proven, it was like this would've been an excellent example for explaining science, why it is difficult to do, and ultimately also help to teach how to think about things critically.

My 8th grade science fair project was measuring how quickly temperature changed depending on the material (used metal bars). I actually wanted to test the difference both in gaining temp, as well as losing temp (my initial test statement was "how quickly does heat and cold travel through various metals?" which is nonsensical really). There was some screwup with the equipment and other things so I ended up getting a sympathy A even though the experiment ended up totally busted.

 

[MrSquished]

My 8th grade science fair project was measuring how quickly temperature changed depending on the material (used metal bars). I actually wanted to test the difference both in gaining temp, as well as losing temp (my initial test statement was "how quickly does heat and cold travel through various metals?" which is nonsensical really). There was some screwup with the equipment and other things so I ended up getting a sympathy A even though the experiment ended up totally busted.

Only thing I remember about science is middle school is that my fat teacher Mrs. Katz accidentally put the final exam, with answers, into a large final project she returned to me. So here I was a period or two later, realizing I had the answer key to the dreaded final. I colluded with my few closest friends and we photocopied the answers and gave them to ourselves. I have no idea how we got caught but we did. I maintained my innocence, which was the truth, that I did not steal any final exam answer key from anyone, it was mistakenly given to me, and that was that. I didn't waver. It was the god's honest truth.

Myself and possibly another person or two, I can't remember, were subsequently banned from the annual 8th grade trip to a local lake, where you could check out all the girls in bikinis. I got to miss out on Debbie L and her amazingly huge tits. Which is all I cared about really. That was the whole punishment.

That's all I remember from science in middle school. That's it.

 

[Charmonium]

A man's gotta have his priorities.

 

[mrblotto]

This came right to mind when I saw the thread title.......go figure

http://www.startrekvids.com/video/28249