Word equations are used to show us a chemical reaction that takes place. For example, if we are told that magnesium reacts with oxygen to form magnesium oxide, we can write the equation:
Magnesium + Oxygen → Magnesium oxide
Mg + O2 → 2MgO
The molecules on the left-hand side of the arrow are the reactants and the molecules on the right-hand side are the products.
There are chemical reactions taking place around us at all times and these chemical reactions lead to chemical changes.
For example, let’s take a look at the combustion of methane. Methane reacts with oxygen (in the air) to form carbon dioxide and water vapour.
This equation can also be shown as the word equation:
Methane + Oxygen → Carbon dioxide + Water
Although the reaction resulted in a chemical change, forming new compounds, there is the same number of each atom on both sides.
This is the same with all chemical reactions. The number of atoms in the reactants is always the same as the number of atoms in the products. This means that the total mass of the reactants is equal to the total mass of the product or products.
So, if the combined mass of the reactants (methane and oxygen) in the equation above equals 100 g, then the combined mass of the products (carbon dioxide and water) must also equal 100 g.