Incomplete Combustion of Organic Compounds
What Is Incomplete Combustion?
- As discussed in the previous section, combustion is a chemical reaction where a fuel reacts with oxygen, releasing energy in the form of heat or light.
- In an ideal scenario, known as complete combustion, hydrocarbons (organic compounds made of carbon and hydrogen) burn in the presence of sufficient oxygen to produce carbon dioxide $CO_2$ and water $H_2O$.
- However, when oxygen is in short supply, incomplete combustion occurs.
- Instead of forming only carbon dioxide and water, incomplete combustion produces harmful byproducts like carbon monoxide $CO$ and elemental carbon $C$, commonly observed as soot.
General Equations for Incomplete Combustion:
- Formation of carbon monoxide:
$$
\text{Fuel} + \text{O}_2 \rightarrow \text{CO} + \text{H}_2\text{O}
$$ - Formation of carbon (soot):
$$
\text{Fuel} + \text{O}_2 \rightarrow \text{C} + \text{H}_2\text{O}
$$
- Formation of carbon monoxide:
$$
2\text{CH}_4 + 3\text{O}_2 \rightarrow 2\text{CO} + 4\text{H}_2\text{O}
$$ - Formation of soot:
$$
\text{CH}_4 + \text{O}_2 \rightarrow \text{C} + 2\text{H}_2\text{O}
$$
Incomplete combustion typically occurs in environments where oxygen is limited, such as car engines, poorly ventilated homes, or industrial furnaces.
Why Does Incomplete Combustion Occur?
Incomplete combustion happens when oxygen becomes the limiting reactant in the reaction. Several factors can contribute to this:
- Poor ventilation:
- In confined or poorly ventilated spaces, oxygen levels may drop below the threshold needed for complete combustion.
- Fuel composition:
- Larger hydrocarbons, with longer and more complex carbon chains, require more oxygen to burn completely and are therefore more prone to incomplete combustion.
- Combustion conditions:
- Low temperatures or insufficient mixing of fuel and oxygen can hinder complete combustion.
Products of Incomplete Combustion
Carbon Monoxide (CO):
- Carbon monoxide is a colorless, odorless, and highly toxic gas.
- It forms when carbon atoms in the fuel are only partially oxidized due to insufficient oxygen.
Why Is Carbon Monoxide Dangerous?
- Carbon monoxide binds tightly and irreversibly to hemoglobin in the blood, forming carboxyhemoglobin.
- This reduces the ability of blood to carry oxygen, leading to symptoms like dizziness, nausea, and, in severe cases, death.
- Students often mistakenly believe that carbon monoxide is "less harmful" than carbon dioxide because it has fewer oxygen atoms.
- In reality, carbon monoxide is far more dangerous due to its ability to disrupt oxygen transport in the body.
