A student writes the following word equation for the reaction between magnesium and oxygen: magnesium + oxygen → magnesium oxide. Describe what a balanced symbol equation shows that a word equation does not, and explain why it is important that a symbol equation is balanced.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A balanced symbol equation shows the chemical symbols / formulae of the reactants and products (rather than just their names)
A balanced symbol equation shows the ratio / number of moles / number of molecules of each reactant and product
A balanced equation is important because atoms are not created or destroyed during a chemical reaction (conservation of mass / atoms)
Therefore the number of each type of atom must be the same on both sides of the equation
A balanced symbol equation shows the ratio / number of moles / number of molecules of each reactant and product
A balanced equation is important because atoms are not created or destroyed during a chemical reaction (conservation of mass / atoms)
Therefore the number of each type of atom must be the same on both sides of the equation
Examiner tips
- Use the word ‘symbol equation’ to show you know the difference from a word equation
- Mention that the symbols give the exact composition of each species
- Explain the conservation of mass in terms of atoms
- Keep the answer concise – 4 points only
Common mistakes
- Writing a balanced equation but not explaining why it matters
- Using the word ‘molecules’ instead of ‘moles’ or ‘atoms’
- Failing to mention the conservation of mass or atoms
Mark scheme (4 marks)
- A balanced symbol equation shows the chemical symbols / formulae of the reactants and products (rather than just their names)
- A balanced symbol equation shows the ratio / number of moles / number of molecules of each reactant and product
- A balanced equation is important because atoms are not created or destroyed during a chemical reaction (conservation of mass / atoms)
- Therefore the number of each type of atom must be the same on both sides of the equation
Key terms in this question
balanced symbol equation · word equation
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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