Aerobic respiration

Cells release energy from nutrient molecules through a series of chemical reactions called aerobic respiration. These reactions use oxygen to break down the nutrient molecules.

When the nutrient is glucose, the overall reactants and products are shown by this word equation:

Glucose and oxygen are the reactants: they are used in the reactions. Carbon dioxide and water are the products: they are formed by the reactions.

Energy is released during the reactions, but it is not a substance, so it is not shown among the products in the word equation.

Balanced chemical equation for aerobic respiration

In aerobic respiration, glucose reacts with oxygen to form carbon dioxide and water. The balanced overall equation is:

The numbers in front of the formulae are coefficients. They show that one glucose molecule reacts with six oxygen molecules to form six carbon dioxide molecules and six water molecules. No coefficient is written in front of glucose because its coefficient is one.

The equation is balanced because it has the same number of atoms of each element on both sides. The coefficients count whole molecules, while the smaller numbers in each formula show the atoms in one molecule.

• Carbon: 6 atoms on each side.
• Hydrogen: 12 atoms on each side.
• Oxygen: 18 atoms on each side: 6 in glucose and 12 in oxygen on the left; 12 in carbon dioxide and 6 in water on the right.