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Chemistry help ... Please

Discussion in 'Science' started by ResourceFinder, Apr 14, 2011.

  1. Hi

    Exothermic reactions

    I understand that breaking bonds is Endothermic because energy needs to be put into the system


    I am unsure why forming bonds is Exothermic ... in my simplistic approach, I need energy to form the bonds so I do not understand why it gives energy out

    Any easy explanation available ... GCSE revision with teen [;(]

    Thanks in advance
  2. the final state [bonded] is a lower energy state than the former.. so when the bond is formed the sytem loses energy
  3. Exothermic reactions give out excess energy as heat. What determines if there is excess energy depends on the bonds being broken and formed. If the energy needed to break the bonds is less than the energy released from forming the bonds, then the reaction is exothermic.
    If the energy needed to break the bonds is more than the energy released from forming the bonds, then the reaction is endothermic.
    (Bond forming releases energy. Atoms will begin with a high potential
    energy, and will bond with other atoms to form compounds which have a
    lower potential energy, and are therefore more stable.)

  4. Thanks both ... so (am I right) before the compound is formed the atoms are reactive and so have potential energy but after they have bonded they are less reactive so have lost potential energy
  5. ps

    My daughter knows the rules (and explained them to me) but neither of us were sure of the why
  6. phlogiston

    phlogiston Star commenter

    If atoms form a covalent bond then the electrons will have arranged with (usually 2) shared electrons holding the atoms together, the energy of these electrons is lower than the energy of unpaired electrons in isolated atoms.
    GCSE level!

  7. I know it is GCSE level ... that is why I am asking
    Thanks for the response

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