Chapter 1 · Chemistry
Chemical Reactions and Equations: Chapter Introduction
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A burning magnesium ribbon leaves only white powder: the same atoms in a new arrangement. How to spot a reaction, write and balance its equation, and name its type.
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Key points
- Burning magnesium gives magnesium oxide: 2Mg + O₂ → 2MgO. The atoms are the same, only rearranged.
- Signs of a reaction: gas given off, colour change, temperature change, precipitate formed (or a change of state).
- A balanced equation has the same number of atoms of each element on both sides (law of conservation of mass).
- Types: combination, decomposition, displacement, double displacement, redox. Everyday effects: corrosion (rusting) and rancidity (chips packets are flushed with nitrogen).
Balancing Mg + O₂ → MgO
| Step | Mg (left / right) | O (left / right) |
|---|---|---|
| Mg + O₂ → MgO | 1 / 1 | 2 / 1 ✗ |
| Mg + O₂ → 2MgO | 1 / 2 ✗ | 2 / 2 |
| 2Mg + O₂ → 2MgO | 2 / 2 ✓ | 2 / 2 ✓ |
Types of reactions
| Type | Pattern | Example |
|---|---|---|
| Combination | A + B → AB | CaO + H₂O → Ca(OH)₂ |
| Decomposition | AB → A + B | CaCO₃ → CaO + CO₂ (heat) |
| Displacement | A + BC → AC + B | Fe + CuSO₄ → FeSO₄ + Cu |
| Double displacement | AB + CD → AD + CB | Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl |
| Redox | oxidation + reduction together | CuO + H₂ → Cu + H₂O |
Quick quiz
3 questions. Choose an answer for each, then submit to see your score and the explanations.