Break It Down: Decomposition
Watch compounds break into simpler substances.
What this lesson covers
Why it matters
Heat a chunk of limestone until it cracks and releases invisible gas. The solid transforms into a new substance while the gas turns limewater milky.
The idea in plain words
Analyze the equation: CaCO₃ → CaO + CO₂. Identify the single reactant and the two products formed by heat.
Predict first
What happens to calcium carbonate when heated strongly?
Thermal decomposition splits one compound into two or more simpler substances using heat.
- It melts into a liquid
- It breaks down into calcium oxide and carbon dioxide — correct
- It stays the same but gets hotter
- It evaporates completely into gas
What you do
Heat the calcium carbonate in a hard-glass boiling tube fitted with a delivery tube. Pass the gas produced through limewater and watch it turn milky.
Check yourself
Which observation confirms carbon dioxide is produced?
Carbon dioxide turns limewater milky due to the formation of insoluble calcium carbonate.
Why is this reaction called thermal decomposition?
Thermal decomposition requires heat to break down a single reactant into multiple products.
- The solid turns black
- Limewater turns milky — correct
- A pop sound is heard
- Because heat breaks one substance into two or more — correct
- Because two substances combine with heat
- Because the substance melts