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Born-Haber Cycle

  1. Apr 25, 2015 #1
    1. The problem statement, all variables and given/known data
    I don't actually need help with an entire problem, I just can't seem to figure out what goes on when an atom is formed from a molecule in a Born-Haber cycle.

    For example:
    The formation of a chlorine atom from a chlorine molecule
    (1/2)Cl2 → Cl(g) ΔH = (1/2) x bond energy of Cl2 = +122 kJ

    2. Relevant equations

    3. The attempt at a solution
    Why is the bond energy being halved? It you have a Cl2 molecule, and you need 244 kJ to break the bond into two Cl atoms. Why would the formation of a Cl atom be only half of that then?
  2. jcsd
  3. Apr 25, 2015 #2
    Doesn't that (1/2) factor mean something?
  4. Apr 26, 2015 #3


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    Science Advisor
    2017 Award

    Here, it might be more useful to think in terms of moles. Reacting one mole of Cl2 takes 244 kJ, and making one mole of chlorine atoms requires reacting 0.5 moles of Cl2.
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