How does methane burn in oxygen to form carbon dioxide and water?

The combustion of methane (CH₄) in oxygen (O₂) is an exothermic reaction that produces carbon dioxide (CO₂) and water. This process is represented by the following balanced chemical equation:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)1

In this reaction, one molecule of methane reacts with two molecules of oxygen to yield one molecule of carbon dioxide and two molecules of water. Because matter is conserved, the total mass of the reactants equals the total mass of the products.1

This reaction releases approximately 900 kilojoules of energy per mole. This energy is released because the chemical bonds in the resulting carbon dioxide and water molecules are stronger and more stable than those in the original methane and oxygen molecules. The decrease in chemical potential energy is typically observed as heat and light, which can be harnessed to perform work, such as in an internal-combustion engine.2