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CHAPTER 1

Chemical Reactions and Equations

Learn how to identify, write and balance chemical equations and classify common reaction types.

Topics in this chapter

  1. Indicators of a chemical reaction
  2. Writing word and skeletal equations
  3. Balancing chemical equations
  4. Combination and decomposition reactions
  5. Displacement and double displacement reactions
  6. Oxidation and reduction
  7. Corrosion and rancidity

Key learning points

✓ A balanced equation has equal numbers of each type of atom on both sides.

✓ State symbols: (s), (l), (g) and (aq).

✓ Oxidation may involve gain of oxygen or loss of hydrogen; reduction is the opposite.

✓ Corrosion is the slow deterioration of metals through reaction with the environment.

Important equations

2Mg + O₂ → 2MgOCaCO₃ → CaO + CO₂Zn + CuSO₄ → ZnSO₄ + CuNa₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl

Multiple-choice questions

1. Which reaction is a decomposition reaction?
  1. CaO + H₂O → Ca(OH)₂
  2. CaCO₃ → CaO + CO₂
  3. Zn + CuSO₄ → ZnSO₄ + Cu
  4. HCl + NaOH → NaCl + H₂O

Answer: B — CaCO₃ → CaO + CO₂

2. The brown coating formed on iron is mainly called:
  1. Rancidity
  2. Rust
  3. Alloy
  4. Slag

Answer: B — Rust

3. In CuO + H₂ → Cu + H₂O, CuO is:
  1. Oxidised
  2. Reduced
  3. Neutralised
  4. Precipitated

Answer: B — Reduced

Very short-answer questions

  1. Why must a chemical equation be balanced?
  2. What does the symbol (aq) indicate?
  3. Name one method used to prevent rancidity.

Short-answer questions

  1. Differentiate between displacement and double displacement reactions with one example each.
  2. Explain oxidation and reduction using a suitable reaction.

Long-answer question

  1. Classify chemical reactions into major types and explain each with balanced equations.