In a chemical reaction, the substances that react together are called reactants and the substances that are made are called products.

Word equations

All reactions can be represented in word equations, which must contain an arrow (→).

reactants → products

For example, when heated, green copper(II) carbonate decomposes into black copper(II) oxide and colourless carbon dioxide gas.

copper(II) carbonate → copper(II) oxide + carbon dioxide

Chemical equations contain an arrow and not an equals sign. The arrow means 'reacts to make'.

Nitrogen and hydrogen react together to form ammonia. Give the word equation for the reaction.

nitrogen + hydrogen → ammonia