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A question regarding combustion

  1. Apr 9, 2013 #1
    In the reaction of H2(g) + O2(g) --> H2O(g) (for example), the H2 doesn't have sufficient energy to overcome the AE to break apart into H+ ions and form H2O molelcules, so a spark is required. In the case of oxygen breaking apart into O2- ions, I'm guessing it does so just to react with the H+ ions because oxygen would rather bond to the hydrogen than be bonded to itself. Is all of this correct, and where is all of the energy being released here? If I had to venture a guess, it would be whenever the water molecule is formed, but I still don't quite understand. to me (a novice) it seems that water would have more potential energy than both the H2 and O2 seeing as the bond is stronger, so more energy would be released in the reverse reaction.


    Sorry if this seems silly but I'm new at this lol.
     
  2. jcsd
  3. Apr 10, 2013 #2

    Borek

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    Staff: Mentor

    Neither H2 breaks into H+ nor O2 breaks into O2-.

    Actually stronger bond means more energy was released. Strong bond means we need to ADD more energy to break it. That in turn means when such bond is created there is more energy given away.
     
  4. Apr 10, 2013 #3
    So what happens then? How does the reaction take place if H2 and O2 aren't broken into ions? Also how do you know if combustion will occur for a molecule or an atom in the first place?
     
  5. Apr 11, 2013 #4

    Borek

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    Staff: Mentor

    They don't have to break into ions, they can go through radicals.
     
  6. Apr 11, 2013 #5
    When H2 and O2 react, for some reason it seemed to me they would have to split apart into ions to combine with each other to form H2O, but acutally the H2(g) and O2(g) split apart and simply form H and O instead of H+ and O2-, correct? And in this unstable state, they find each other and react to release a large amount of energy. The spark is required to overcome the activation energy, and once it does, a chain reaction occurs reacting the remaing H2 and O2?

    As for the question I asked earlier about knowing when an element or molecule will combust, when two substances react, some sort of energy is always released whether it's heat, light, electrical, etc. But how do know which type of energy is going to be released? Is there any way to know this without experimentaton? And is there any way you can tell how much energy is going to be released without knowing the standard state enthalpy and entropy of the reactants and products?
     
    Last edited: Apr 11, 2013
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