Lesson 5 of 13
One becomes many
Show on a big screenLimestone is calcium carbonate. Limestone gives a gas and quicklime, calcium oxide. The push is the energy that starts the split.
Step 1 of 3
- Calcium carbonate: one group.
- Heat is the push.
- Two groups form: calcium oxide and carbon dioxide. CaCO₃ → CaO + CO₂.
Read each split. Tap the push: heat, light or electricity.
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The rule
A decomposition reaction splits one reactant into two or more products. Heat, light or electricity usually gives the push.
It is the opposite of a combination reaction.
A split by heat is thermal decomposition. A split by light is photolytic. A split by electricity is electrolytic.
Each split below takes in energy. A reaction that takes in energy is endothermic.
| The substance | The push | Splits into |
|---|---|---|
| Calcium carbonate | heat | calcium oxide and carbon dioxide |
| Baking soda | heat | sodium carbonate, water, carbon dioxide |
| Silver chloride | light | silver and chlorine |
| Water | electricity | hydrogen and oxygen |
- CaCO₃ → CaO + CO₂
- 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
- 2AgCl → 2Ag + Cl₂
- 2H₂O → 2H₂ + O₂
Silver bromide splits in light too. Black-and-white photography uses this.
Try the lab to finish this lesson.