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Nitrogen oxide formation during combustion
This question is about burning fuels in central heating boilers.
Explain how oxides of nitrogen are produced when burning fuels.
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Marking points
- 1 Identifies the high temperature during combustion.
- 2 Explains that this causes nitrogen and oxygen from the air to react.
Full-mark answer
Burning the fuel produces a high temperature. At this temperature, nitrogen and oxygen from the air react to form oxides of nitrogen.
Why this answer loses marks
Nitrogen in the fuel burns and turns directly into nitrogen oxides.
The credited route uses nitrogen and oxygen from the air reacting at the high temperature produced by combustion.