Fossil fuels — coal, petroleum, and natural gas — are hydrocarbons formed over millions of years from the remains of organisms. They are non-renewable and their combustion is the primary source of atmospheric CO₂.
Complete vs Incomplete Combustion
Complete Combustion
Excess oxygen present:
CH₄ + 2O₂ → CO₂ + 2H₂O
- Produces CO₂ and H₂O
- Releases maximum energy
- Blue flame
Incomplete Combustion
Insufficient oxygen:
2CH₄ + 3O₂ → 2CO + 4H₂O
- Produces CO (toxic) or C (soot)
- Releases less energy
- Yellow/orange flame
Pollution from Fossil Fuels
| Pollutant | Source | Effect |
|---|---|---|
| CO₂ | Complete combustion | Greenhouse gas → climate change |
| CO | Incomplete combustion | Toxic — binds to haemoglobin |
| SO₂ | Sulphur impurities in fuel | Acid rain (H₂SO₄) |
| NOₓ | High-temperature combustion (cars) | Acid rain, photochemical smog |
| Particulates | Soot (carbon) | Respiratory disease, reduced visibility |
Think About It
Catalytic converters in car exhausts reduce CO and NOₓ emissions. What chemical reactions might occur inside them?
2CO + 2NO → 2CO₂ + N₂. The catalyst (Pt, Pd, Rh) allows CO to reduce NO at lower temperatures, converting two harmful gases into less harmful products.