Decomposition reactions
Consider the second reaction of activity 16.2. There potassium permanganate decomposes on heating into other compounds and an element.
potassium permanganate → potassium manganate + manganese dioxide + oxygen
2KMnO4 → K2MnO4 + MnO2 + O2
The sign Δ over the arrow shows that the reaction needs heat.
Decomposition reaction
A compound decomposing into simpler compounds, into elements, or into compounds and elements together is called a chemical decomposition reaction.
A → B + C
Three more examples
calcium carbonate → calcium oxide + carbon dioxide
CaCO3 → CaO + CO2
silver oxide → silver + oxygen
2Ag2O → 4Ag + O2
hydrogen peroxide → water + oxygen gas
2H2O2 → 2H2O + O2
The opposite of combination
A decomposition reaction always has exactly one reactant. If there is only one substance on the left-hand side, it is a decomposition.
Two of these three examples produce oxygen — we meet them again in section 16.5 as laboratory methods of preparing it.