Given the bond energies below, calculate an estimate for ΔH (kJ) for the reaction: 2CO (g) + O2 (g) - > 2CO2 (g) Bond energy (kJ/mol) : C-O, 360; C=O, 799; CO (triple bond), 1071; O2, 498

The enthalpy change estimate will be given by the expression:

ΔH = ∑ Energies of the bonds broken - ∑ Energies of the bond formed

So what we need to do is an inventory of the bond broken and formed, and compute the ΔH.

To do that we need first the balanced chemical equation:

2 CO (g) + O₂ (g) ⇒ 2 CO₂ (g)

Bonds broken (kJ) Bonds Formed (kJ)

2 C≡O 2 (1071) 2 C=O 2 (799)

1 O=O 498

ΔH (kJ) = 2 (1071) + 498 - 2 (799) = 1042 kJ

Notice we were given the bond energy for C-O, but in this problem we did not form a C-O or break a C-O bond. Be careful to choose the correct value, especially when using reference tables.