A word equation names the reactants on the left and the products on the right, with an arrow between them. It is the first step before writing symbols, and questions often ask for it alone. This lesson comes before ionic equations, and it makes balancing easier because you decide the substances first.
It belongs to the formulas and equations module.
How do I read a description?
Underline three things in the description. First, what is present at the start. Second, what is made at the end.
Third, any words that are only conditions, such as “heated”, “in the presence of a catalyst” or “at room temperature”. Conditions do not appear as reactants.
How to write the equation, step by step
- List the starting substances by name.
- List the substances formed by name.
- Put reactants on the left and products on the right, joined with + signs.
- Draw one arrow, from left to right.
- Keep conditions off the substance list. Write them above the arrow if the question wants them.
Worked example
Zinc carbonate is heated and breaks down. A solid zinc oxide remains and a gas, carbon dioxide, is given off. Write the word equation. (This is an invented teaching scenario.)
Step 1, starting substance: zinc carbonate. “Heated” is a condition, not a reactant.
Step 2, substances formed: zinc oxide and carbon dioxide.
Step 3 and 4:
zinc carbonate → zinc oxide + carbon dioxide
The word “heat” may be written above the arrow. It must not be written on the left as if it were a substance.
The mistake to watch for
A common slip is to treat a condition as a reactant.
Mistaken answer: zinc carbonate + heat → zinc oxide + carbon dioxide
The student wrote “heat” as if it were a substance that reacts.
Heat is the condition that makes the change happen. It belongs above the arrow, or can be left out. The correct answer is zinc carbonate → zinc oxide + carbon dioxide.
Check yourself
1. Copper(II) oxide reacts with dilute sulfuric acid to form a blue solution of copper(II) sulfate. Water is also formed. Write the word equation.
Show answer
Reactants: copper(II) oxide and sulfuric acid. Products: copper(II) sulfate and water.
copper(II) oxide + sulfuric acid → copper(II) sulfate + water
2. Magnesium ribbon reacts with dilute hydrochloric acid, giving off a gas and leaving a solution of magnesium chloride. Write the word equation.
Show answer
A metal with an acid forms a salt and hydrogen.
magnesium + hydrochloric acid → magnesium chloride + hydrogen
3. Calcium carbonate is heated strongly and breaks down into a solid oxide and carbon dioxide. Write the word equation.
Show answer
The solid oxide is calcium oxide. “Heated strongly” is a condition only.
calcium carbonate → calcium oxide + carbon dioxide
Where this leads next
Once naming is secure, move on to identifying a spectator species in an ionic equation. The equation balance reasoning trainer helps when you turn these names into symbols.
If you know the reaction families but still mix up sides, a teacher in online one-to-one Chemistry tuition can build a quick sorting routine with you.