Atoms, elements and compounds: write word equations for the reactions in this specification

The idea

A word equation names the reactants and products of a chemical reaction, with an arrow showing the direction of change. You write the names of the starting substances on the left, separated by a plus sign where there is more than one, then an arrow, then the names of the substances formed on the right, again separated by plus signs. For example, magnesium reacting with oxygen is written as magnesium + oxygen → magnesium oxide. The names must be the correct chemical names, not everyday labels, and the equation must account for every reactant and product in the reaction described. Word equations apply to all the reactions named in the specification, including combustion, neutralisation, displacement, precipitation and reactions of acids with metals and carbonates.

What earns the marks

• Reactant names are written on the left of the arrow and product names on the right, in the correct order.
• A plus sign separates each pair of substances on the same side of the arrow.
• The arrow, not an equals sign, shows the direction of the reaction.
• Chemical names are used accurately, for example magnesium oxide rather than magnesium ash.
• Every substance named in the reaction is included, so no reactant or product is omitted.
• State symbols are not required in a word equation, but the names must match the substances actually reacting.

Common mistakes and how to put them right

• Writing products on the left and reactants on the right.

  Put it right by checking that the substances you start with are always on the left.

• Using an equals sign instead of an arrow.

  Put it right: Replace it with → to show the direction of change.

• Naming a product incorrectly, such as writing sodium chloride as sodium chlorine.

  Put it right by using the proper compound name formed from the elements involved.

Exam tips

• Underline the chemical names in the question before writing so you do not miss a reactant or product.
• Check that each name is a real chemical substance and that the elements in it match those in the reactants.
• Practise the common reactions from the specification, such as acid + metal → salt + hydrogen, until the naming pattern is automatic.