Lesson focus: A word equationA way of writing a reaction using the names of the substances, such as "magnesium + oxygen → magnesium oxide". communicates which substances react and which substances form without claiming particle numbers.
Construct, interpret and check word equations using accurate substance names.
Build on earlier learning
Chemical reactionsThe previous lesson identified reactants and products; this lesson represents them symbolically.
You will be successful when you can…
- Place reactants and products correctly.
- Use plus signs and one reaction arrow.
- Use substance names rather than descriptions.
- Infer a missing substance from a reaction pattern.
Words that carry the science
- word equation
- A reaction representation using substance names.
- reaction arrow
- A symbol meaning reacts to form.
- reactant
- A starting substance written left of the arrow.
- product
- A formed substance written right of the arrow.
- coefficient
- A number placed before a formula in a balanced symbol equation.
The arrow separates start and finish
01The arrow separates start and finish
Write reactantA substance you start with in a chemical reaction. on the left, productA new substance made in a chemical reaction. on the right, plus signs between substances and one arrow meaning “react to form”.
Use precise substance names: “magnesium oxide” rather than “white powder”. State symbols and conditions belong to more detailed equations, not ordinary word equationA way of writing a reaction using the names of the substances, such as "magnesium + oxygen → magnesium oxide"..
02Reaction patterns help predict products
Patterns include metal + oxygen → metal oxide, acid + metal → salt + hydrogen, and acid + carbonate → salt + water + carbon dioxide.
Patterns support predictions only when the reactants fit. The salt name depends on both the metal or base and the acid.
03Word and symbol equations do different jobs
A word equation checks chemical names and reaction pattern. A symbol equation additionally shows formulae and particle ratios.
When balancing symbol equations, change coefficientA big number in front of a formula in an equation that tells you how many of that particle there are, such as the 2 in 2H₂O. only. Changing a formula subscript changes substance identity.
Build an acid–metal equation
Magnesium reacts with hydrochloric acid.
- Identify reactants: magnesium and hydrochloric acid.
- Use the pattern acid + metal → salt + hydrogen.
- Hydrochloric acid produces a chloride salt.
- Write magnesium + hydrochloric acid → magnesium chloride + hydrogen.
How to make the reasoning visible: Every substance is named and placed on the correct side.
Complete reaction patterns
Use names and patterns rather than guessing from appearance.
| Reactant 1 | Reactant 2 | Product pattern | Missing product |
|---|---|---|---|
| copper | oxygen | metal oxide | ? |
| zinc | hydrochloric acid | salt + hydrogen | ? |
| calcium carbonate | nitric acid | salt + water + carbon dioxide | ? |
| sulfuric acid | sodium hydroxide | salt + water | ? |
Complete all products.
Why must copper oxide not be written as copper + oxygen on the product side?
Check your understanding
Answer from memory, then check against the suggested answer.
Where are reactants written?
What does the arrow mean?
Which salt comes from nitric acid?
Write the word equation for calcium reacting with oxygen.
Why must formula subscripts never be changed to balance an equation?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Construct the word equation for the reaction.
(3)sulfuric acid + → +
Identify the gas produced.
(1)Total for this question: 4 marks
Command word: For constructA command word: draw or build something, such as a table or graph, using the correct layout., use exact substance names and one correctly directed arrow.