ACS Organic Chemistry Practice Test

Combustion is a type of oxidation where a fuel reacts with an oxidizer to form carbon dioxide and water, releasing energy. For a hydrocarbon, the usual pattern is a fuel plus oxygen giving CO2 and H2O: CxHy + O2 → x CO2 + (y/2) H2O. The given equation shows reactants containing carbon and hydrogen (the fuel) and products that are water and carbon dioxide, which is the hallmark of complete combustion. It captures the essential outcome of burning a fuel: production of CO2 and H2O. The other patterns represent different types of reactions—combination, displacement, or decomposition—not combustion. In a fully balanced depiction, oxygen gas would appear on the reactant side, but the core idea is clear from the products formed.