Which of the following represents complete combustion of a hydrocarbon with sufficient oxygen?

Which of the following represents complete combustion of a hydrocarbon with sufficient oxygen?

• A. CO2 and H2O
• B. CO and H2O
• C. C and H2O
• D. CH4 and O2

Answer: (A)

When a hydrocarbon burns with plenty of oxygen, it undergoes complete combustion, producing carbon dioxide and water. This happens because the carbon atoms are fully oxidized to CO2 and the hydrogen atoms are fully oxidized to H2O, as long as there is more than enough oxygen available. In other words, the products are the most oxidized forms of the elements contained in the fuel. This is why CO2 and H2O are the correct products. The other possibilities indicate different outcomes: carbon monoxide and water would arise if oxygen were insufficient, leaving carbon only partially oxidized; elemental carbon and water would imply carbon is left as solid soot, which also signals incomplete combustion; and CH4 plus O2 are reactants, not products, so they describe the starting materials rather than the products of combustion.

When a hydrocarbon burns with plenty of oxygen, it undergoes complete combustion, producing carbon dioxide and water. This happens because the carbon atoms are fully oxidized to CO2 and the hydrogen atoms are fully oxidized to H2O, as long as there is more than enough oxygen available. In other words, the products are the most oxidized forms of the elements contained in the fuel.

This is why CO2 and H2O are the correct products. The other possibilities indicate different outcomes: carbon monoxide and water would arise if oxygen were insufficient, leaving carbon only partially oxidized; elemental carbon and water would imply carbon is left as solid soot, which also signals incomplete combustion; and CH4 plus O2 are reactants, not products, so they describe the starting materials rather than the products of combustion.