Here are some of the examples of the second-order chemical reactions which are not balanced because some of the following reactions are intermediate reactions of some another reactions.
H+ + OH– → H2O
Inthis above reaction hydrogen ion and hydroxyl ions form water.
O + O3 → O2 + O2
During combustion reaction, oxygen atom and ozone can form oxygen molecules.
O2 + C → O + CO
Another combustion reaction, in this oxygen molecules react with carbon to form oxygen atoms and carbon monoxide.
NH4CNO → H2NCONH2
Ammonium cyanate in water isomerizes into urea.