Estimate Using bond enthalpies

Question

Estimate ΔH_rxn for the following chemical reaction using the bond enthalpies in the table found here. Report your answer to zero decimal places in standard notation (i.e. 123. kJ *For numbers ending in zero, be sure to include the decimal!*).

C₂H₅Br(g) + HBr(g) → C₂H₆(g) + Br₂(g)

Answer 1

On the reactant side, you need to break

1 C-Br bond = +284 kJ/mol

1 H-Br bond = +364 kJ/mol

TOTAL = + 648 kJ/mol

On the product side, you need to form

1 C-H bond = -414 kJ/mol

1 Br-Br bond = -193 kJ/mol

TOTAL = - 607 kJ/mol

∆Hrxn = 648 - 607 = 41 kJ