AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
The gases released into the atmosphere when a fuel is burned may include…
Full specification wording
Atmospheric pollutants from fuels: The gases released into the atmosphere when a fuel is burned may include carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen.
Burning a fuel releases a mixture of gases into the atmosphere.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 3 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Burning a fuel releases a mixture of gases into the atmosphere. Carbon dioxide and water vapour form when carbon and hydrogen in the fuel are oxidised completely. If oxygen is limited, incomplete combustion also produces carbon monoxide, a toxic gas. Sulfur impurities in the fuel burn to sulfur dioxide. At the high temperatures inside engines and furnaces, nitrogen and oxygen from the air react to form oxides of nitrogen. For example, a car engine burning petrol can release carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and nitrogen oxides in its exhaust. The word may is important because the exact mixture depends on the fuel, the oxygen supply and the temperature.
What earns the marks
- Carbon dioxide is released when carbon in a fuel is oxidised.
- Water vapour is released when hydrogen in a fuel is oxidised.
- Carbon monoxide is released when a fuel burns in a limited supply of oxygen.
- Sulfur dioxide is released when sulfur impurities in a fuel burn.
- Oxides of nitrogen are released when nitrogen and oxygen from the air react at high temperatures.
- The gases released depend on the fuel composition, oxygen supply and combustion temperature.
Common mistakes and how to put them right
Listing carbon monoxide as a product of complete combustion.
Put it right: Carbon monoxide forms during incomplete combustion when oxygen is limited.
Saying that oxides of nitrogen come from nitrogen in the fuel.
Put it right: They form from nitrogen and oxygen in the air at high temperatures.
Treating water vapour as a pollutant gas in the same way as carbon monoxide or sulfur dioxide.
Put it right: Water vapour is a normal combustion product, while the other named gases cause specific pollution problems.
Exam tips
- For each gas, give both its name and how it is formed, because marks often depend on linking the gas to its source.
- Use the word may when listing exhaust gases, since the mixture varies with fuel and conditions.
- If asked to name pollutant gases from burning a named fuel, check the fuel composition first so you include sulfur dioxide only when sulfur is present.
Try the lesson
The start of the Atmospheric pollutants from fuels: The gases released into the atmosphere when a fuel is burned may include carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen. lesson, made from checked teaching notes for this specification point.
Have a go first
Which gas released when a fuel burns in plenty of air is a greenhouse gas formed from the carbon in the fuel?
Listen
Burning a fuel releases a mixture of gases into the atmosphere. Carbon dioxide and water vapour form when carbon and hydrogen in the fuel are oxidised completely. If oxygen is limited, incomplete combustion also produces carbon monoxide, a toxic gas. Sulfur impurities in the fuel burn to sulfur dioxide. At the high temperatures inside engines and furnaces, nitrogen and oxygen from the air react to form oxides of nitrogen. For example, a car engine burning petrol can release carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and nitrogen oxides in its exhaust. The word may is important because the exact mixture depends on the fuel, the oxygen supply and the temperature. A strong answer earns marks for these points. Carbon dioxide is released when carbon in a fuel is oxidised. Water vapour is released when hydrogen in a fuel is oxidised. Carbon monoxide is released when a fuel burns in a limited supply of oxygen. Sulfur dioxide is released when sulfur impurities in a fuel burn. A common slip: Listing carbon monoxide as a product of complete combustion. Instead, carbon monoxide forms during incomplete combustion when oxygen is limited. Exam tip: For each gas, give both its name and how it is formed, because marks often depend on linking the gas to its source.
See it
Key words
Say what each word means before you turn the card.
Products of combustion
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Incomplete combustion
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Oxides of nitrogen
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Variable exhaust composition
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See every definition
- Products of combustion
- The gases released into the atmosphere when a fuel is burned may include carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen.
- Incomplete combustion
- When oxygen is limited, this produces carbon monoxide, a toxic gas.
- Oxides of nitrogen
- At the high temperatures inside engines and furnaces, nitrogen and oxygen from the air react to form these.
- Variable exhaust composition
- The exact mixture depends on the fuel, the oxygen supply and the temperature, which is why the word may is important.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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