2) Breaking covalent bonds always requires the input of energy and forming them always releases
energy. The following table shows the bond energies of some covalent bonds, this is the amount
of energy required to break the bonds as well as the amount of energy released when the bonds
form. Use the information in the table to determine whether the reactions are endothermic or
exothermic. (The structural formulae might help with this, feel free to look these up online.)
a) CH4(g) +202(g) → CO2(g) + 2H2O (g)
ΔΗ =
b) CO(g) + 2H2(g) → CH3OH(1)
c) 2H2O(g) → 2H2(g) + O2(g)
-
d) 2H2(g) + O2(g) → 2H2O(g)
Bond
H-H
H-F
C-H
C-0
C=O
C-C
C-CI
Table 1 Average Bond Energies (kJ/mol)
Energy
432
565
413
ΔΗ =
ΔΗ –
358
1072
347
339
AH =
Bond
F-F
O-H
CI-CI
C-C
C=O
C-O (for CO₂(g))
0-0
Energy
154
467
239
614
745
799
495