A question regarding combustion

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    Combustion
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Discussion Overview

The discussion revolves around the combustion reaction of hydrogen and oxygen to form water, focusing on the mechanisms involved, the energy changes during the reaction, and the conditions necessary for combustion. Participants explore concepts related to activation energy, bond formation, and the nature of reactants and products in combustion processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that H2 requires a spark to overcome activation energy to break apart into H+ ions for the formation of water, questioning the energy release during the reaction.
  • Another participant challenges the notion that H2 and O2 break into ions, stating that stronger bonds release more energy when formed, implying a misunderstanding of the bond energy concept.
  • A follow-up question arises about how the reaction occurs if H2 and O2 do not break into ions, prompting inquiries about the conditions for combustion.
  • It is proposed that H2 and O2 can form radicals instead of ions, suggesting an alternative pathway for the reaction.
  • Further clarification is sought regarding the nature of the reaction, with a participant asserting that H2 and O2 split into H and O rather than ions, and that a chain reaction occurs after the initial spark.
  • Questions are raised about predicting the type and amount of energy released during combustion without experimental data or knowledge of standard state enthalpy and entropy.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of the combustion reaction, particularly regarding the role of ions and radicals. There is no consensus on how to predict energy release in combustion reactions without experimentation.

Contextual Notes

Participants exhibit uncertainty regarding the definitions of ions and radicals in the context of combustion, as well as the implications of bond strength on energy release. The discussion reflects a range of assumptions about the nature of chemical reactions and energy transformations.

aclark609
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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.
 
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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.
 
Borek said:
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.

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?
 
They don't have to break into ions, they can go through radicals.
 
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 remaining 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?
 
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