A chemical reaction is a transformation of a group of chemicals called reactants to another group of chemicals called products. A combustion is a chemical reaction that releases a lot of energy (usually heat) in a short amount of time. Combustion reactions are at the heart of many industrial processes.

A combustion reaction is written in the form of an equation with the reactants on the left and the products on the right. The arrow indicates the direction of the reaction.

Since the work of Lavoisier in 1770 we have known that mass is conserved for all chemical transformations. The Law of Conservation of Mass states that the number of atoms of each element is the same on both sides of the equation. For that reason, it is always necessary to find the coefficients that allow the equation to be balanced.

For the combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O
For the combustion of ethane: 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O
For the combustion of propane: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O