Combustion (A): fire, oxides and methane

With plenty of oxygen, a hydrocarbon burns completely to carbon dioxide and water. For methane, the main gas in natural gas: CH₄ + 2O₂ → CO₂ + 2H₂O + heat. When there is too little oxygen the combustion is incomplete. Then some carbon ends up as carbon monoxide, CO, a toxic gas, or as soot, which is carbon: 2CH₄ + 3O₂ → 2CO + 4H₂O, and CH₄ + O₂ → C + 2H₂O. Soot is unburnt carbon, not smoke from dirt, and carbon monoxide is a compound of carbon and oxygen, not a form of carbon. Burning the same mass of fuel incompletely gives less heat than burning it completely. A gas burner with its air hole open has a blue flame, which is the hotter and more complete burning. With the hole nearly closed the flame turns yellow and makes soot. To balance an equation, count each kind of atom on both sides and add whole-number coefficients until the counts match. Fuel burners must never be used in a closed room without ventilation: ask an adult.