# Is this example of Bond Energy correct?

1. Sep 2, 2017

### esale

1. The problem statement, all variables and given/known data

(see attachments for example 2.9)

2. Relevant equations

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. Sep 2, 2017

### esale

And Table 2.2

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

### mjc123

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.

4. Sep 12, 2017