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AQA GCSE · Question 05.1 · Chemistry of the atmosphere
This question is about burning fuels in central heating boilers. In the future, gas central heating boilers may burn hydrogen rather than natural gas. Table 2 shows information about these fuels when 1 dm³ of the fuel is burned in a central heating boiler.
Explain how oxides of nitrogen are produced when burning fuels.
This question is about burning fuels in central heating boilers. In the future, gas central heating boilers may burn hydrogen rather than natural gas. Table 2 shows information about these fuels when 1 dm³ of the fuel is burned in a central heating boiler.
Explain how oxides of nitrogen are produced when burning fuels.
How to approach this question
The question asks how oxides of nitrogen (NOx) are formed during combustion.
1. Think about what is present during combustion in a boiler. There is the fuel and there is air.
2. What are the main gases in the air?
3. The fuel itself doesn't contain nitrogen. So where does the nitrogen for the oxides of nitrogen come from?
4. What condition inside a boiler or engine allows these normally unreactive gases from the air to react?
Full Answer
Oxides of nitrogen, often abbreviated as NOx (e.g., NO, NO₂), are atmospheric pollutants. They are not typically formed from the fuel itself, but from the air used in the combustion process. Air is approximately 78% nitrogen (N₂) and 21% oxygen (O₂). Normally, nitrogen is a very unreactive gas due to the strong triple bond in the N₂ molecule. However, the very high temperatures and pressures inside a combustion engine or a central heating boiler provide enough energy to break these strong bonds. This allows nitrogen and oxygen from the air to react with each other, forming various oxides of nitrogen.
Common mistakes
✗ Stating that the nitrogen comes from the fuel.
✗ Forgetting to mention the essential condition of high temperature.
✗ Just saying "from the air" without specifying which gases from the air react.
Practice the full AQA GCSE Chemistry Higher Tier Paper 2
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