A word equation names the reactants and products: magnesium + oxygen → magnesium oxide. A symbol equation uses chemical formulae and must be balanced.
Step-by-Step Balancing Method
- Write the unbalanced equation with correct formulae: Mg + O₂ → MgO
- Count atoms on each side: Left: 1 Mg, 2 O. Right: 1 Mg, 1 O. Oxygen is unbalanced.
- Add coefficients (big numbers) in front of formulae — never change the subscripts inside a formula: 2Mg + O₂ → 2MgO
- Check again: Left: 2 Mg, 2 O. Right: 2 Mg, 2 O. Balanced.
Golden Rule: You can only add coefficients in front of formulae. You must NEVER change the subscripts inside a formula to balance an equation — that would create a different substance.
State Symbols
State symbols are added in brackets after each formula to show the physical state:
- (s) — solid
- (l) — liquid
- (g) — gas
- (aq) — aqueous solution (dissolved in water)
Example with state symbols: 2Mg(s) + O₂(g) → 2MgO(s)
This deep dive covers Word Equations and Symbol Equations within Formulae, Equations and Conservation of Mass for GCSE Chemistry. Revise Formulae, Equations and Conservation of Mass in Quantitative Chemistry for GCSE Chemistry with 13 exam-style questions and 12 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 4 of 14 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Formulae, Equations and Conservation of Mass
Which of the following is the correct formula for oxygen gas?
Explain why mass is conserved in a chemical reaction.