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Fuels, combustion and acid rain
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Burning hydrocarbon fuels releases heat, but can also release poisonous and acidic gases.
Complete and incomplete combustion
A fuel is a substance that releases heat energy when burned.
Complete combustion (plenty of oxygen): carbon dioxide and water. CH4 + 2O2 → CO2 + 2H2O
Incomplete combustion (limited oxygen): carbon monoxide and/or carbon (soot), and water.
Complete combustion (plenty of oxygen): carbon dioxide and water. CH4 + 2O2 → CO2 + 2H2O
Incomplete combustion (limited oxygen): carbon monoxide and/or carbon (soot), and water.
Why carbon monoxide is poisonous
Carbon monoxide combines with haemoglobin in red blood cells.
This reduces the capacity of the blood to carry oxygen, so cells are starved of oxygen.
It is colourless and has no smell, so it is hard to detect.
This reduces the capacity of the blood to carry oxygen, so cells are starved of oxygen.
It is colourless and has no smell, so it is hard to detect.
Nitrogen oxides, sulfur dioxide and acid rain
In car engines, the temperature is high enough for nitrogen and oxygen from the air to react, forming oxides of nitrogen.
Some fuels contain sulfur impurities, which burn to form sulfur dioxide.
Both gases dissolve in rainwater to form acid rain, which damages limestone buildings and trees and makes lakes acidic.
Some fuels contain sulfur impurities, which burn to form sulfur dioxide.
Both gases dissolve in rainwater to form acid rain, which damages limestone buildings and trees and makes lakes acidic.
Why does a car engine release nitrogen oxides, even though petrol contains no nitrogen?
- The nitrogen comes from the air drawn into the engine.
- The engine is very hot, so nitrogen and oxygen react.
Answer: At the high temperature in the engine, nitrogen and oxygen from the air react together.
A fuel releases heat when burned. Complete combustion gives carbon dioxide and water; incomplete gives carbon monoxide and soot. Carbon monoxide reduces the blood's ability to carry oxygen. Hot engines make nitrogen oxides; sulfur impurities make sulfur dioxide; both cause acid rain.
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