When 1.0 mol of H2O2 decomposes to form H2O and O2, 103 kJ of energy is released. Given the bond energies below, what is the bond energy of the O-O single bond in H2O2?

Bond Energy for H-O: 463 kJ/mol
Bond Energy for O=O: 498 kJ/mol

The answer is +146 kJ/mol, could someone please explain why? Thank you!

1 Answer
Jan 27, 2018

Determine what bonds must be broken, those are energy costs. Determine what bonds are formed, those are energy rebates. The sum is ∆H


H2O2 has two O-H bonds and one O-O bond

H2O has two O-H bonds

O2 has one O=O bond

2H2O2-->2H2O + O2 + 206 kJ

During reaction there is no net change in the number of O-H bonds
During reaction two O-O bonds are broken : ? kJ
During reaction one O=O bond is formed: -498 kJ
Since 498 kJ of energy are released during formation of O=O and the balanced reaction shows only 206 kJ are released, it must have cost (498kJ -206kJ) = 292kJ to break the 2 O-O bonds, so it was 292kJ/2 for each or 146kJ