Answer:
The answer is b), -228 kJ
Explanation:
First, we consider which bonds are broken and formed during the reaction
Broken, Br - Br (02 molecules), C ≡ C
Formed, C - C, C - Br (4 bonds)
Noted that when breaking bonds, the molecules NEED energy, while forming bond, they release energy. So, secondly, we calculate
Breaking energy = 2 x (Br-Br) + 1 x (C≡C) = 2 x 193 + 1 x 837 = 1,223 kJ
Forming energy = - (4 x (C-Br) + 1 x (C-C) = - (4 x 276 + 1 x 347) = - 1,451 kJ (minus means that the energy is released during the reaction)
Hence the ΔH°ᵣₓₙ is 1,223 kJ + (-1,451) kJ = - 228 kJ