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Combustion of Methane Endothermic or Exothermic?
The combustion of methane is an exothermic process. The energy content of the methane is greater than the energy content of the carbon dioxide and water which will be produces by the chemical reaction.
Combustion reaction produce products which have a lower energy state than the reactants which were present before the reaction.
A fuel (sugar for example) has a great deal of chemical potential energy. When the sugar burns by reacting with oxygen, it produces mostly water and carbon dioxide. Both water and carbon dioxide are molecules which have less stored energy than what sugar molecules have.
Here is a video which discusses how to calculate the change when 0.13g of butane is burned. Video from: Noel Pauller