Grade 10 Physical Sciences · Chemical Change

Balance a chemical equation

Add numbers in front of formulae so the atoms on both sides match (2H₂ + O₂ → 2H₂O).

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Balancing Reactions Grade 10Kevinmathscience

How to Balance Chemical Equations in 5 Easy Steps: Balancing Equations TutorialWayne Breslyn (Dr. B.)

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Question 4.5 · May/June 2025 · Paper 2 · National (DBE) · 3 marks

In the flow diagram below, a primary alcohol P is used as a starting reactant to form different organic compounds under different reaction conditions. Diagram for this question

4.5 Write down a balanced equation using MOLECULAR FORMULAE for the complete combustion of butane.(3)

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

More past paper questions: balance a chemical equation

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3. Question 7.1.5 · November 2025 · Paper 2 · National (DBE) · 3 marks
7.1 Phosphoric acid, $H_{3} PO_{4}$ (aq), is an example of an acid that can ionise in three steps, as shown below.

$H_{3} PO_{4} (aq) + H_{2} O (ℓ) ⇌ H_{3} O^{+} (aq) + H_{2} PO_{4}^{-} (aq)$ $K_{a} = 6, 9 \times 1 0^{- 3}$
$H_{2} PO_{4}^{-} (aq) + H_{2} O (ℓ) ⇌ H_{3} O^{+} (aq) + HPO_{4}^{2 -} (aq)$ $K_{a} = 6, 2 \times 1 0^{- 8}$
$HPO_{4}^{2 -} (aq) + H_{2} O (ℓ) ⇌ H_{3} O^{+} (aq) + PO_{4}^{3 -} (aq)$ $K_{a} = 4, 8 \times 1 0^{- 13}$

Answer the questions that follow.
7.1.5 Write a balanced equation to explain the answer to QUESTION 7.1.4.(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants $HPO_{4}^{2 -} (aq) + H_{2} O (ℓ)$
  1 mark · Write acid-base reaction equations
2. ✓
  Products $H_{2} PO_{4}^{-} (aq) + OH^{-} (aq)$
  OR $H_{3} PO_{4} (aq) + 2 OH^{-} (aq)$
  1 mark · Write acid-base reaction equations
3. ✓
  Balancing $HPO_{4}^{2 -} (aq) + H_{2} O (ℓ) ⇌ H_{2} PO_{4}^{-} (aq) + OH^{-} (aq)$
  OR $HPO_{4}^{2 -} (aq) + 2 H_{2} O (ℓ) ⇌ H_{3} PO_{4} (aq) + 2 OH^{-} (aq)$
  1 mark · Balance a chemical equation
4. Question 6.3 · November 2024 · Paper 2 · Provincial · 2 marks
6.3 Balance the following reaction equation:

$NH_{3} (g) + O_{2} (g) \to NO(g) + H_{2} O(ℓ)$ (2)
Show the memo (2 ticks)Memo
1. ✓
  Reactant coefficients $4 NH_{3} (g) + 5 O_{2} (g)$
  1 mark · Balance a chemical equation
2. ✓
  Product coefficients $\to 4 NO(g) + 6 H_{2} O(ℓ)$
  1 mark · Balance a chemical equation
5. Question 2.2.5 · May/June 2023 · Paper 2 · National (DBE) · 3 marks
Study the table below and answer the questions that follow.
2.2 Write down the:
2.2.5 Balanced equation, using MOLECULAR FORMULAE, for the complete combustion of compound A(3)
Show the memo (3 ticks)Memo
1. ✓
  Correct molecular formula: C8H18 $2 C_{8} H_{18}$ + ...
  1 mark · Draw structural formulae
2. ✓
  Correct molecular formulae of the inorganic reactant and products $... + 25 O_{2} \to 16 CO_{2} + 18 H_{2} O$
  1 mark · Write a chemical equation
3. ✓
  Balancing $2 C_{8} H_{18} + 25 O_{2} \to 16 CO_{2} + 18 H_{2} O$
  1 mark · Balance a chemical equation
6. Question 4.1.3 · November 2023 · Paper 2 · National (DBE) · 3 marks
4.1 Consider the cracking reaction below.

$C_{16} H_{34} \to C_{6} H_{14} + C_{6} H_{x} + 2 C_{y} H_{z}$
Compound $C_{6} H_{14}$ undergoes complete combustion.
4.1.3 Using MOLECULAR FORMULAE, write down the balanced equation for this reaction.(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactant: $O_{2}$ $2 C_{6} H_{14} + 19 O_{2}$
  1 mark · Write a chemical equation
2. ✓
  Products $\to 12 CO_{2} + 14 H_{2} O$
  1 mark · Write a chemical equation
3. ✓
  Balancing $2 C_{6} H_{14} + 19 O_{2} \to 12 CO_{2} + 14 H_{2} O$
  1 mark · Balance a chemical equation

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