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Chemical Reaction Changes Color Over and Over

Posted by timothy on from the note-gratuitous-but-accurate-dig dept.

DancingFountain writes "If you have taken a college chemistry class, you may have seen this fantastic demonstration. When two clear liquids are mixed, they immediately turn yellow, and then undulate back and forth between blue-black and yellow in a mesmerizing display. Wired Science explains that the reaction, which was developed by two high school science teachers, has been rigorously studied but not fully explained."

13 of 61 comments (clear)

  1. Huh? by moosesocks · · Score: 3, Interesting

    I'm confused..... where's the news here?

    The reaction's notable for its cyclical nature and the fact that we don't really understand the underlying mechanisms. According to the news article, we still haven't figured it out.

    Thanks for that status update!

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    1. Re:Huh? by moosesocks · · Score: 4, Informative

      Uhm. No.

      Perpetual motion machines are flat-out impossible. Conservation of energy is a *VERY* well established scientific fact.

      Chemical reactions don't necessarily release heat. Endothermic reactions tend to absorb it. The reaction mechanism here just happens to end up with a large amount of its original reactants at the end, and most likely catalyzes itself somewhere along the way.

      The reaction in question isn't exactly perpetual either. The system eventually reaches equilibrium, and the cycle stops. (Entropy -- another well-established scientific principle makes perpetual motion rather unlikely)

      If you wanted to harvest energy from the reaction, you'd have to directly absorb it from the system as the reaction is taking place. This alters the system, and will most likely result in the reaction stopping, assuming that the temperature differential is great enough to allow you to harvest any useful amount of energy (I don't recall this particular reaction getting very hot, so that seems unlikely). You'd also be limited by the second law of thermodynamics and the carnot efficency probably wouldn't be all that favorable.

      So, all in all, the reaction's rather novel, although there's nothing in our current understanding of scientific fact that dictates that it should be impossible, even though we haven't been able to piece together the exact mechanism by which the reaction actually takes place.

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    2. Re:Huh? by Mr2cents · · Score: 3, Informative

      The wired article itself does not provide much information, but one of its' links, more specifically this one explains a lot (including the reactions). It does say that is does not go on for ever, but repeats for "just" 15 cycles or more. It would have been cool if it went on forever, but no such luck.

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    3. Re:Huh? by Zaurus · · Score: 4, Funny

      Perpetual motion machines are flat-out impossible. ...unless you're raising a toddler.
    4. Re:Huh? by fireboy1919 · · Score: 3, Insightful

      Conservation of energy is a *VERY* well established scientific fact.

      No. Conservation is a law - a postulate. Something that we're extremely certain that can't prove using other laws, but that has never, ever been wrong once. That is the fact. If we found something that violated this law, then it would no longer be considered a law. Personally, I don't consider overwhelming evidence that something has always happened a particular way within the observation of man proof that it always did or always will. Don't get me wrong: I'd never take a bet that a perpetual motion machine is going to work, but I'm not going to go around believing that reality is 100% certain to work the way that I think it does, either.

      The system eventually reaches equilibrium, and the cycle stop

      Apparently goes through about 10 cycles, according to Wikipedia.

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    5. Re:Huh? by paintballer1087 · · Score: 3, Interesting

      And that's impossible. I mean science has always gotten everything right about physics. Don't belive those crazy rumors going around that the world is spherical.... As much as we know about physics, astronomy, matter, time, space, etc... There's that much more that we don't know. I'm not saying perpetual motion is something that will ever be discovered, or if it is possible. But saying something is "impossible" because we would be wrong otherwise, puts us at the place of knowing everything. As far as we know, the second law of thermodynamics is right, but we've been proven wrong in the past, and probably will in the future.

    6. Re:Huh? by ceoyoyo · · Score: 3, Funny

      That's not perpetual motion. Have you noticed you're more tired since you had him? The energy has to come from somewhere you see. It just seems really impressive because you're big and he's little so when you put your energy in a little package it moves much faster.

  2. i remember this from high school by circletimessquare · · Score: 4, Informative

    it has to do with the fact that instead of the usual equilibrium present in a reaction, there are two, or three equilibriums between three or four different states, all roughly equivalent thermodynamically. they just seesaw around in circles between the equilibriums when a little energy is introduced into the mix. apparently its very tricky to get it just right. but if you do, the equilbriums bounce back and forth between each other like a pendulum or spring, and sometimes, balanced just right, like a pendulum on a grandfather clock, they can bounce back and forth for a very long time

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  3. Re:Just had to slip one in? by framauro13 · · Score: 5, Funny

    It's ok. Republican's don't believe in science. He'll never read this.

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  4. WHAT ... is your favorite colour? by Colin+Douglas+Howell · · Score: 3, Funny

    Yellow. No, blue--AAAAAAAAHHH!

    [Too bad the movie has the colors in the opposite order.]

  5. Direct Video Link by Erioll · · Score: 3, Informative

    Here's a video of it on google video: http://video.google.com/videoplay?docid=680106771263243162

  6. News from before you were born. by siglercm · · Score: 3, Funny

    I knew I had seen something like this in an article I read... THIRTY YEARS AGO...

    http://amasci.com/amateur/sciamdx.html

    Search for "Chemical reactions, oscillating".

    Sorry, kiddies. Been there, done that. Still interesting, though.

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  7. oscillating reactions are reasonably well known by StandardDeviant · · Score: 3, Interesting

    I did a math paper for a mathematical modeling class during my chemistry undergrad on the BZ reaction mechanism, which is another oscillator like the system in TFA. It's not a perpetual oscillation, but with precisely controlled reagents you can get some pretty long-lasting oscillations (precisely as in on the order of hundredths of a mole, iirc). There's a really good little book in the oxford chemistry primers series (series as a whole is quite nice for accessible, focused introductions to various fields) on this topic: Oscillations, Waves, and Chaos in Chemical Kinetics by Scott.

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