IB Chemistry R1.3 Notes

We use fuels everywhere such as to power our cars and our homes. Fuels, which are typically hydrocarbons, such as coal, oil or gas release energy to provide us with the necessary heat and power via complete combustion. This is a  highly exothermic reaction that produces heat and requires oxygen. Complete combustion of fuels occurs with excess oxygen and produces carbon dioxide and water. For example, pentane (C₅H₁₂) combusts as follows:

C₅H₁₂ + 8O₂ → 5CO₂ + 6H₂O

Alcohols can also undergo complete combustion under the same conditions to form Carbon Dioxide and water. For example, Ethanol (C₂H₅OH) combusts as follows:

C­₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

When oxygen is limited, combustion is called incomplete. The products of incomplete combustion are Carbon (soot), carbon monoxide and water. The IB wants you to determine equations for the incomplete combustion of alcohols and hydrocarbons. The products of the reaction are identical, only the balancing has to be practiced.

Methane:

3CH₄ + 4O₂ → C + 2CO + 6H₂O

Ethanol:

C_2​H₅​OH + 2O₂​ → 2CO + 3C (soot) + 3H₂​O

Carbon monoxide is an incredibly poisonous gas and incomplete combustion can therefore be detrimental to health. Carbon monoxide can bind to haemoglobin and limit oxygen supply to organs.