## 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

### Tauria

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. $2HgO_{s} \xrightarrow{\text{heat}} 2Hg_{l} + O_{2g}$