[miss.strw]

Using average bond enthalpy values estimate ΔH (kJ/mol) for the following gas phase reaction. (Use Table 8.2) ( Should you need it, the ΔH for N=0 is 607 kJ/mol).

CH2=CH2 + Br2 --> CH2BrCH2Br

How come this is wrong : attempt

C-H = 4x416 = 1664
C=C = 1x598 = 598
Br-Br = 1x193 = 193
Energy needed = 2455 kJ

C-H = 4x416 = 1664
C-Br = 2x285 = 570
C-C = 1 X 347 = 347
Energy released = 2581 kJ

1664+570 + 347 = 2581

2581-2455 = 126

ΔH = - 126 kJ

[UG]

Your method looks correct. I have not done the maths