Word Equation – IGCSE Chemistry Definition and Key Facts
IGCSE Chemistry definition of word equation: a way of representing a chemical reaction using the full names of reactants and products. Covers rules, examples, and converting to symbol equations.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Word equations are the starting point for representing chemical reactions in the Cambridge 0620 syllabus. While Paper 4 focuses on balanced symbol equations, Paper 2 and Paper 1 frequently ask for word equations. Writing them correctly is a basic skill that underpins all equation work.
The 0620 definition
A word equation is a representation of a chemical reaction that uses the names of the reactants and products rather than their chemical formulae.
Reactants → Products
The arrow means “reacts to form” or “produces.” It is not an equals sign.
Rules for writing word equations
- Reactants go on the left of the arrow
- Products go on the right of the arrow
- A + sign separates multiple reactants or multiple products
- Use the correct chemical names — not common names (say “calcium carbonate” not “limestone”)
- State symbols (s), (l), (g), (aq) are not used in word equations — they belong in symbol equations only
Core word equations to know
Acid reactions
| Word equation | Type |
|---|---|
| acid + metal → salt + hydrogen | Metal-acid reaction |
| acid + base → salt + water | Neutralisation |
| acid + alkali → salt + water | Neutralisation |
| acid + carbonate → salt + water + carbon dioxide | Carbonate-acid reaction |
Combustion
| Word equation | Type |
|---|---|
| hydrocarbon + oxygen → carbon dioxide + water | Complete combustion |
| hydrocarbon + oxygen → carbon monoxide + water | Incomplete combustion |
| hydrocarbon + oxygen → carbon + water | Incomplete combustion (very limited O₂) |
Metal reactions
| Word equation | Type |
|---|---|
| metal + oxygen → metal oxide | Oxidation |
| metal + water → metal hydroxide + hydrogen | Group I metals |
| metal + acid → salt + hydrogen | Displacement of hydrogen |
Other important reactions
| Word equation | Type |
|---|---|
| metal carbonate → metal oxide + carbon dioxide | Thermal decomposition |
| metal oxide + carbon → metal + carbon dioxide | Reduction of an ore |
Converting word equations to symbol equations
Paper 4 often provides a word equation and asks candidates to write the balanced symbol equation. The steps:
- Write the word equation
- Replace each name with the correct chemical formula
- Count atoms on each side
- Add coefficients to balance the equation
- Check that every element balances
Example
Word equation: calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
Symbol equation: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
Naming salts from word equations
When writing the product salt in a word equation, combine:
- The metal name from the base/metal/carbonate
- The ending from the acid used
| Acid | Salt ending |
|---|---|
| Hydrochloric acid | chloride |
| Sulfuric acid | sulfate |
| Nitric acid | nitrate |
Example: zinc + sulfuric acid → zinc sulfate + hydrogen
Worked exam question
Write word equations for: (a) the reaction of sodium hydroxide with hydrochloric acid [1], (b) the thermal decomposition of copper(II) carbonate [1], (c) the complete combustion of methane [1].
(a) sodium hydroxide + hydrochloric acid → sodium chloride + water [1]
(b) copper(II) carbonate → copper(II) oxide + carbon dioxide [1]
(c) methane + oxygen → carbon dioxide + water [1]
Common exam mistakes
- Writing formulae in a word equation — use names only. “HCl + NaOH → NaCl + H₂O” is a symbol equation, not a word equation.
- Getting the salt name wrong — “sodium hydrochlorate” or “copper sulfuric” instead of sodium chloride and copper sulfate.
- Missing a product. The reaction of acid with carbonate produces three products (salt + water + carbon dioxide) — forgetting CO₂ loses a mark.
- Using an equals sign instead of an arrow. The arrow (→) shows the direction of the reaction and is standard in chemistry.
- Writing “calcium” instead of “calcium carbonate” for a specific compound — use the full compound name, not just the metal.
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