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Heat of atomization

  1. Apr 20, 2015 #1
    1. The problem statement, all variables and given/known data
    The heat of atomization of methane and ethane are 360kJ/moo and 620kJ/mol, respectively.
    The longest wavelength of light capable of breaking the C-C bond is (Avogadro number = 6.02 x 1023, h= 6.62 x 1034J s

    2. Relevant equations
    E = hν = hc/λ
    3. The attempt at a solution
    I think we should consider energy of ethane only as it only has C-C bond.
    What is the use of methane energy?
     
  2. jcsd
  3. Apr 20, 2015 #2

    Borek

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    Staff: Mentor

    What bonds are present?
     
  4. Apr 20, 2015 #3
    methane is CH4 and ethane is C2H6. All are single bonds.
     
  5. Apr 20, 2015 #4

    Borek

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    Let me rephrase the question: bonds between what atoms are present?
     
  6. Apr 20, 2015 #5
    Bonds between carbon and hydrogen are present in methane and in ethane between carbon and carbon and also carbon and hydrogen.
     
  7. Apr 20, 2015 #6

    Borek

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    So you have two kinds of bonds. Methane contains only one kind, ethane contains two kinds. Within a good approximation bond energy doesn't depend on the molecule.
     
  8. Apr 20, 2015 #7
    So now what should I do?
    Take E = 360 kJ/mol ?
     
  9. Apr 20, 2015 #8

    Borek

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    360 kJ/mol is required to break how many bonds between which atoms? How much per this particular kind of bond is it?
     
  10. Apr 20, 2015 #9
    To break 4 C-H bond we require 360 kJ. For 1 C-H bond it is 90 kJ.
    For 6 C-H it is 540 kJ.
    So for ethane, heat of atomization is 620 kJ.
    So for C-C bond it is 90 kJ/ mol
    For 1 C-C bond it is 90 / (6.02 x 1023) kJ
     
  11. Apr 20, 2015 #10
    Hi!!!
    4 (C-H) bonds require 360kJ/mol....to break them
    1×C-C bond+6(C-H) bonds require 620 KJ/mol.
    So you can find C-C bond energy.
     
  12. Apr 20, 2015 #11
    Thanks all of you, got it.
    Mooncrater I think we had written the posts at same time, so you don't realized my 9th post?
     
  13. Apr 20, 2015 #12
    Yup...you're absolutely right..heehee tech sometimes messes things up:)
     
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