Decomposition Reactions

11SCI - Chemical Reactions

Finn LeSueur


Mahi Tuatahi

  1. Give the general equation for:
    • A precipitation reaction
    • A displacement reaction
    • A combination reaction
  2. Give an observation that you might make to indicate that each type of reaction has occurred.

Ngā Whāinga Ako

  • To describe what happens in a decomposition reaction.

Decomposition Reactions

\[\begin{aligned} AB \xrightarrow{heat} A + B \end{aligned}\]
  • A reaction where one compound is split apart to form two products. It is the reverse of combination and a lot of energy is required for the reaction to occur.
  • Metal carbonates decompose to metal oxide and carbon dioxide gas


Mercury (II) oxide is heated in a test tube. The solid is seen to change colour and a gas is given off.

  1. If the gas is oxygen, how could you confirm this?
  2. Write a word equation.
  3. Write a symbol equation (with states) and balance it.
  1. A glowing splint in the presence of oxygen gas, will reignite.
  2. mercury oxide \(\xrightarrow{\text{heat}}\) mercury + oxygen gas
  3. \(2HgO_{s} \xrightarrow{\text{heat}} 2Hg_{l} + O_{2g}\)