Hydrocarbon + oxygen → carbon dioxide + water
Here are the equations for the complete combustion of propane, used in bottled gas:
Propane + oxygen → carbon dioxide + water
C3H8 + 5O2 → 3CO2 + 4H2O
Write a balanced equation for the complete combustion of methane, CH4, found in natural gas.
CH4 + 2O2 → CO2 + 2H2O
Incomplete combustion happens when the supply of air or oxygen is poor. Water is still produced, but carbon monoxide and carbon are also produced. Less energy is released than during complete combustion.
For example, here is one possible equation for the incomplete combustion of propane:
Propane + oxygen → carbon monoxide + carbon + water
C3H8 + 3O2 → 2CO + C + 4H2O
Notice that fewer oxygen molecules are needed to balance the equation than are needed for the complete combustion of propane.
The carbon is released as fine black particles. We see this in smoky flames and it is deposited as soot. Soot can cause breathing problems and it blackens buildings. It may block boilers and other appliances, or cause a fire.
Carbon monoxide is a toxic gas. It is absorbed in the lungs and binds with the haemoglobin in the red blood cells. This reduces the capacity of the blood to carry oxygen. Carbon monoxide causes drowsiness, and affected people may fall unconscious or even die.