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Thermal Decomposition year 8 Chemistry
🔥 Thermal Decomposition – Year 8
Complete Lesson Notes with Questions & Answers
🎥 Watch & Learn: Thermal Decomposition Explained!
📌 What is Thermal Decomposition?
Definition: A thermal decomposition reaction is a chemical reaction in which a compound breaks down into two or more simpler substances when heated.
Thermal = heat
Decomposition = breaking down
So, thermal decomposition means breaking down using heat.
📌 General Form
Compound → (heat) → Substance A + Substance B
It is the opposite of a combination reaction.
🔬 Example 1: Calcium Carbonate
[Insert Images of Calcium Carbonate Heating Experiment Here]
CaCO₃ (s) → (heat) → CaO (s) + CO₂ (g)
- Calcium oxide (solid)
- Carbon dioxide (gas)
Q1. What does thermal mean?
Heat.
Q2. What happens to a compound in decomposition?
It breaks into simpler substances.
Q3. Name the gas produced when CaCO₃ is heated.
Carbon dioxide (CO₂).
🧪 Example 2: Copper Carbonate
[Insert Images of Copper Carbonate Heating Here]
CuCO₃ (s) → (heat) → CuO (s) + CO₂ (g)
Observations:
- Green solid turns black
- Carbon dioxide gas is released
Q4. What colour change is seen?
Green to black.
Q5. What solid is formed?
Copper oxide (CuO).
📌 Key Points to Remember
- Heat is always required
- A single compound breaks down
- Usually produces a gas
- It is an endothermic reaction
Q6. Is thermal decomposition exothermic or endothermic?
Endothermic.
Q7. Why does it need heat?
To break chemical bonds.
📝 Practice Questions – Easy
1. Define thermal decomposition.
A reaction where a compound breaks down into simpler substances using heat.
2. Write the word equation for calcium carbonate decomposition.
Calcium carbonate → Calcium oxide + Carbon dioxide
3. What type of substance is broken down?
Compound.
📝 Practice Questions – Medium
4. MgCO₃ → (heat) → ____ + ____
MgO + CO₂
5. What gas turns limewater milky?
Carbon dioxide.
6. Why do metal carbonates release CO₂?
Because carbonates break down into metal oxides and carbon dioxide.
📝 Practice Questions – Challenging
7. A white solid produces gas turning limewater milky. What is it?
A metal carbonate.
8. Why is it not a physical change?
Because new substances are formed.
9. Which is thermal decomposition?
A) H + O → Water
B) CaCO₃ → CaO + CO₂
C) Iron + Oxygen → Rust
B) CaCO₃ → CaO + CO₂
C) Iron + Oxygen → Rust
B
📊 Summary Table
| Feature | Thermal Decomposition |
|---|---|
| Energy Needed | Heat |
| Type of Reaction | Endothermic |
| What happens? | Compound breaks down |
| Example | CaCO₃ → CaO + CO₂ |
🏁 Final Check Quiz
- What does decomposition mean?
- Is heat absorbed or released?
- Name one carbonate that decomposes.
- What test confirms CO₂?
- Write one symbol equation.
1. Breaking down
2. Absorbed
3. Calcium carbonate / Copper carbonate
4. Limewater turns milky
5. CaCO₃ → CaO + CO₂
2. Absorbed
3. Calcium carbonate / Copper carbonate
4. Limewater turns milky
5. CaCO₃ → CaO + CO₂