The OO and OO bond energies are 146 and 496 kJmol respective

The O-O and O=O bond energies are 146 and 496 kJ/mol, respectively, and those of S-S and S=S are 226 and 423 kJ/mol. Using this data, discuss which would be thermodynamically more stable: (a) Cyclooctasulfur, S_8, or four diatomic S_2 molecules? (b) Cyclooctaoxygen, O_8, or four diatomic O_2 molecule?

Solution

a) S8 has 8 S-S bonds

hence Total energy required to break all bonds in S8 = 8 x S-S bond energy = 8 x ( 226) = 1808 KJ

4 S2 moles total energy required to break all bonds = 4 x S=S bond energy = 4 x 423 = 1692 KJ

Thus S8 is more stable than 4 S2 bonds since it requires more energy to break all bonds in S8 than in 4S2

b) Total energy required to break all bonds in O8 = 8 x O-O energy   = 8 x 146 = 1168 KJ

Total energy required to break 4 O2   = 4 x O=O Bond energy = 4 x 496 = 1984 KJ

Thus it requires more energy to break 4 O2 than O8 , hence 4 O2 is ore stable