Incomplete Combustion of Hydrocarbons and Alcohols
Quick Notes
- Complete combustion occurs when oxygen supply is in excess of fuel
- Incomplete combustion occurs when oxygen supply is limited.
- Produces carbon monoxide (CO) and/or carbon (C) instead of carbon dioxide.
- Typical products: CO, H2O, or C (soot) and H2O.
- Common with hydrocarbons and alcohols in oxygen-poor environments.
- Toxic CO binds to hemoglobin and reduces oxygen transport in the body.
- Write balanced equations showing alternative carbon-containing products.
Full Notes
Complete vs. Incomplete Combustion
There are two types of combustion that can occur when hydrocarbons are burned in oxygen – complete and incomplete.
Complete combustion occurs when there is enough oxygen present and carbon can be fully oxidised, forming carbon dioxide as a product (and water).
Example:
Complete Combustion of methane: CH4 + 2O2 → CO2 + 2H2O
Incomplete combustion occurs when there is limited oxygen present and carbon can’t be fully oxidised, meaning carbon monoxide (CO) or carbon (soot) gets formed as a product (and water).
Example:
Incomplete Combustion of methane:
CH4 + 1.5O2 → CO + 2H2O
CH4 + O2 → C + 2H2O
Why It Matters
Ensuring complete combustion occurs is important for several reasons:
- Carbon Monoxide (CO) is poisonous and can be fatal when inhaled due to its ability to prevent oxygen binding to haemoglobin in red blood cells, limiting the amount of oxygen that the blood can transport.
- Soot (carbon) contributes to pollution and respiratory issues.
- Incomplete combustion is less energy-efficient than complete combustion, meaning less energy is released per kg of fuel than for complete combustion.
Summary
- Incomplete combustion happens when oxygen supply is limited.
- It produces CO and/or soot instead of only CO2.
- CO is poisonous as it binds to haemoglobin and prevents oxygen transport.
- Soot contributes to pollution and respiratory problems.
- Incomplete combustion releases less energy than complete combustion.
What might be observed when a fuel such as methane is burned in a limited supply of oxygen?
In a limited supply of oxygen, incomplete combustion occurs. Instead of forming only CO2 and H2O, products like carbon monoxide (CO) or even carbon (soot) are formed. This may be observed as a yellow, smoky flame instead of a clean blue flame.
How does limiting the supply of oxygen in combustion affect the products and increase health risks?
When oxygen is limited, incomplete combustion occurs, producing carbon monoxide (CO) and sometimes soot (carbon particles) instead of carbon dioxide. Carbon monoxide is toxic, as it binds to haemoglobin more strongly than oxygen, reducing oxygen transport in the body and posing serious health risks.