The reaction between methane (CH₄) and oxygen (O₂) is an exothermic combustion reaction, which releases energy in the form of heat and light. The balanced chemical equation for this reaction is:
CH4+2O2→CO2+2H2O+energy
Under normal conditions, methane and oxygen do not react spontaneously because, like many chemical reactions, this combustion reaction has an activation energy barrier. Activation energy is the minimum energy needed to break the bonds in the reactants and initiate the reaction. In the case of methane and oxygen, the molecules need an initial input of energy to overcome this activation energy.
Simply mixing methane and oxygen does not provide enough energy for the reaction to start. However, when a burning matchstick is introduced, it provides the necessary activation energy. The heat from the matchstick is enough to break the bonds in the methane molecules and the oxygen molecules, allowing the reaction to proceed. Once the reaction begins, it becomes self-sustaining because the combustion of methane releases a significant amount of heat, which is enough to keep the reaction going without further input of energy from an external source like the matchstick.
The reaction continues until one or both reactants (CH₄ or O₂) are consumed, and the products—carbon dioxide (CO₂) and water (H₂O)—are formed. The exothermic nature of the reaction ensures that once it starts, the energy released helps to drive the reaction to completion.