Grade 10 Physical Sciences · Chemical Change

Write a chemical equation

Write the correct formulae for the reactants and products of a reaction (hydrogen + oxygen → water as H₂ + O₂ → H₂O).

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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)

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More past paper questions: write a chemical equation

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3. 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
4. Question 2.4.2 · May/June 2022 · Paper 2 · National (DBE) · 3 marks
The letters A to H in the table below represent eight organic compounds.
2.4 For compound G, write down:
2.4.2 A balanced equation, using molecular formulae, for its complete combustion(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants $2 C_{4} H_{10} + 13 O_{2}$
  1 mark · Write a chemical equation
2. ✓
  Products $\to 8 CO_{2} + 10 H_{2} O$
  1 mark · Write a chemical equation
3. ✓
  Balancing $2 C_{4} H_{10} + 13 O_{2} \to 8 CO_{2} + 10 H_{2} O$
  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 WE4 · Siyavula Grade 10 Physical Sciences, 14.2 Balancing chemical equations, Worked example 4 · 3 marks
WE4 Solid zinc metal reacts with aqueous hydrochloric acid to form an aqueous solution of zinc chloride ( $ZnCl_{2}$ ) and hydrogen gas. Write a balanced equation for this reaction.(3)
Show the memo (3 ticks)Memo
1. ✓
  Reactants and productsReactants: zinc ( $Zn$ ) and hydrochloric acid ( $HCl$ ). Products: zinc chloride ( $ZnCl_{2}$ ) and hydrogen ( $H_{2}$ ).
  $Zn + HCl \to ZnCl_{2} + H_{2}$
  1 mark · Write a chemical equation
2. ✓
  BalanceTwo Cl atoms on the right and one on the left, so give HCl a coefficient of $2$ :
  $Zn + 2 HCl \to ZnCl_{2} + H_{2}$
  1 mark · Balance a chemical equation
3. ✓
  State symbols $Zn (s) + 2 HCl (aq) \to ZnCl_{2} (aq) + H_{2} (g)$
  1 mark · Write a chemical equation

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