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Homework Help: Chemical reaction of 2 H atoms.

  1. Oct 11, 2004 #1
    2 H atoms can form a H2 molecule, releasing energy of 5 eV. However, no chemical reaction occurs when 2 isolated H atmos collide! Explain this curious result using the conservation laws.

    first of all, i don't know what conservation law to use for this question.
    2nd i think i don't have much knowledge on chemistry.
    third i can't relate this problem to physics...

    if 2 H atoms can for H2 molecule, when there are many H atoms...
    then why can't 2 isolated H atoms form H2 molecule?

    can anyone just explain...
  2. jcsd
  3. Oct 11, 2004 #2
    i would guess that this has something to do with the ativation energy required to form the H2 molecule.

    In order for molecules to be formed they need activation evergy to start the process.

    Perhaps this curious thing of 2 H molecules colliding is merely the problem that their speeds are no sufficiently high
  4. Oct 11, 2004 #3
    Then how can it gain more velocity when there is more hydrogen atoms
  5. Oct 11, 2004 #4


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    You know (have ben given) that H2 + 5 eV -> 2H. An isolated pair of monatomic hydrogen atoms combine according to the reverse, 2H -> H2 + 5 eV. Looks kinda like we're moving in circles, doesn't it? Where are you going to put the 5 eV in the isolated case? The point of the question is that you are to see that there is a necessity for "third bodies" or "moderators" to carry energy to/from reacting atoms or molecules in most reaction mechanisms.
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