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Combustion, pollutants and cracking
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Burning fuels releases energy and some harmful pollutants. Cracking turns long hydrocarbons into more useful short ones.
Combustion
Complete combustion (plenty of oxygen): hydrocarbon + oxygen → carbon dioxide + water.
Incomplete combustion (limited oxygen): also makes carbon monoxide (toxic) and soot (carbon particles).
Incomplete combustion (limited oxygen): also makes carbon monoxide (toxic) and soot (carbon particles).
Pollutants
Sulfur dioxide (from sulfur impurities) and nitrogen oxides (from N2 and O2 reacting in hot engines) cause acid rain.
Hydrogen is a cleaner fuel: it only produces water, but is hard to store.
Hydrogen is a cleaner fuel: it only produces water, but is hard to store.
Cracking
Long-chain alkanes are heated with a catalyst to break them into shorter alkanes and alkenes.
Short chains are in higher demand as fuels; alkenes are used to make polymers.
Short chains are in higher demand as fuels; alkenes are used to make polymers.
Why is carbon monoxide dangerous?
- It binds to haemoglobin in red blood cells.
- Less oxygen is carried around the body.
- It is colourless and odourless, so hard to detect.
Answer: It stops blood carrying oxygen.
Complete combustion makes CO2 and water; incomplete also makes CO and soot. SO2 and NO_x cause acid rain. Cracking breaks long alkanes into shorter alkanes and alkenes.
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