How to estimate (Delta H) for the bromination of ethylene from bond dissociation energies ?
This problem is an application of Hess's Law.
We break all the bonds to form atoms, and then we reassemble the atoms to form new bonds.
The equation is
H₂C=CH₂ + Br-Br → Br-CH₂-CH₂-Br
We can ignore the C-H bonds, because they are just being broken and re-formed.
We need a table of bond energies like the one below.