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Looking for intuition on exothermic reactions

  1. Apr 7, 2017 #1
    All,

    I am looking for a logical step that I must be missing in order to understand how heat energy is produced in an exothermic reaction. All of the standard explanations--more heat is given off than is taken in--don't seem satisfying. If heat is the result of the kinetic energy of molecules, how does the creation of new, more stable bonds produce this kinetic energy in the surroundings? I hope this makes sense. I cannot understand how the molecules forming new bonds are imparting this kinetic energy to their neighboring molecules.
     
  2. jcsd
  3. Apr 7, 2017 #2

    DrClaude

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    Be careful here. This is a common, but often misleading picture. At a given temperature, energy is distributed among all degrees of freedom, not just kinetic energy (look up the equipartition theorem).

    Following from what I wrote above, the extra energy does not necessarily go immediately into kinetic energy. When a bond breaks, you can get bits flying off with more kinetic energy, but you can also get an excited molecule where the conversion to kinetic energy will take, e.g., collisions with other molecules.
     
  4. Apr 7, 2017 #3

    hilbert2

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    It's about electromagnetic potential energy being converted to kinetic energy in the form of random motion of the molecules. Just like the potential and kinetic energy of a falling meteorite is converted to heat when it comes down.

    EDIT: yes, initially some of the released energy can be in the form of sound waves but even them quickly turn into heat by viscous dissipation.
     
  5. Apr 7, 2017 #4
    Thanks for the replies. One source seems to suggest that as more stable bonds are forming, the electrostatic forces between these atoms are accelerating them together and thus increasing the kinetic energy of their surroundings, too. Would this be an accurate description?
     
  6. Apr 7, 2017 #5

    DrClaude

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    Somewhat. The bonds will not be formed in their ground state, and that vibrational excitation will eventually be transferred to the surroundings. (But again, I strongly advise against thinking of "heat" as "kinetic energy." They are not the same thing.)
     
  7. Apr 7, 2017 #6
    Hmm, thanks. I definitely need more reading on this. What do you recommend I look up to investigate heat in forms that is not kinetic energy?
     
  8. Apr 7, 2017 #7

    DrClaude

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  9. Apr 8, 2017 #8

    Ygggdrasil

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    Here's my attempt at a simplified explanation in a previous thread (https://www.physicsforums.com/threa...-energy-get-lower-as-atoms-get-closer.897854/):
    The transfer of vibrational energy from the bond to the surrounding molecules is how an exothermic reaction can transfer heat to the surrounding.
     
  10. Apr 12, 2017 #9
    In an exothermic reaction heat is evolved as the molecules gain stability to form compound.
     
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