Using average bond energy values estimate ΔH for the following gas phase reaction.?

Question

CH2=CH2 + Br2 → BrCH2CH2Br

Answer 1

In your text, you'll have the table of bond enthalpies. In this reaction, you will break a Br-Br bond and a C=C bond. You will form 2 C-Br bonds and will form a C-C bond.

Add the values for the bonds formed (exothermic) and for the bonds broken (endothermic), and you've got your answer...