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Homework Help: Is this example of Bond Energy correct?

  1. Sep 2, 2017 #1
    1. The problem statement, all variables and given/known data

    ex2_10.JPG
    (see attachments for example 2.9)

    2. Relevant equations

    be_equation.JPG

    3. The attempt at a solution
    As far as I have read and understood, most polymerizations (such as the one in this example) are exothermic. If this is the case, shouldn't this produce a negative (-) reaction energy? And the equation they should have used is the one I included in section two (2)?

    Thank you in advance for any help.

    -E
     
  2. jcsd
  3. Sep 2, 2017 #2
    Forgot to add example 2.9...

    ex2_9.jpg

    And Table 2.2

    table2_2.JPG
     
    Last edited by a moderator: Sep 2, 2017
  4. Sep 4, 2017 #3

    mjc123

    User Avatar
    Science Advisor

    Unless they are defining "reaction energy" differently from usual, the blue box is wrong. You input the energy to break the C=C bond, and the energy of forming two C-C bonds is given out. So the enthalpy change is +680 - 740 = -60 kJ/mol. They may be confused by the fact that
    ΔHrxn = Hproducts - Hreactants
    But this is not equal to BEproducts - BEreactants
    Relative to the state where all bonds are broken, H = -BE. So your white box is right.
     
  5. Sep 12, 2017 #4
    Thank you for your answer!
     
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