Is this example of Bond Energy correct?

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Discussion Overview

The discussion revolves around the concept of bond energy in the context of polymerization reactions, specifically examining an example provided in the homework. Participants are analyzing whether the reaction energy is correctly represented and the implications of bond energies in the calculation of enthalpy changes.

Discussion Character

  • Homework-related
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant asserts that most polymerizations are exothermic and questions whether this should result in a negative reaction energy.
  • Another participant challenges the interpretation of "reaction energy," suggesting that the calculation presented in the example may be incorrect based on standard definitions of enthalpy change.
  • There is a discussion about the relationship between bond energies and enthalpy changes, with one participant emphasizing that the enthalpy change is not equal to the difference in bond energies of products and reactants.
  • One participant expresses agreement with the correction of the example's representation of bond energies and enthalpy changes.

Areas of Agreement / Disagreement

Participants express differing views on the correct interpretation of reaction energy and bond energies, indicating that the discussion remains unresolved with multiple competing perspectives on the calculations involved.

Contextual Notes

There are potential limitations regarding the definitions of terms like "reaction energy" and the assumptions made in the calculations, which have not been fully clarified in the discussion.

esale

Homework Statement


[/B]
ex2_10.JPG

(see attachments for example 2.9)

Homework Equations


[/B]
be_equation.JPG


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
 
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Forgot to add example 2.9...

ex2_9.jpg


And Table 2.2

table2_2.JPG
 
Last edited by a moderator:
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.
 
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mjc123 said:
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.

Thank you for your answer!
 

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