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This question is about combustion of fuels - AQA - GCSE Chemistry - Question 5 - 2019 - Paper 2
Question 5
This question is about combustion of fuels. Some central heating boilers use wood as a fuel. Suggest two reasons why wood is more sustainable than natural gas as a... show full transcript
Worked Solution & Example Answer:This question is about combustion of fuels - AQA - GCSE Chemistry - Question 5 - 2019 - Paper 2
Step 1
Suggest two reasons why wood is more sustainable than natural gas as a fuel for central heating boilers.
Answer
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Wood is a renewable resource, meaning it can be replanted and regrown, while natural gas is finite and will deplete over time.
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Burning wood is carbon-neutral, as it releases the same amount of carbon dioxide that the trees absorbed during their life cycle, whereas burning natural gas increases the net carbon dioxide in the atmosphere.
Step 2
Explain the process by which carbon monoxide can be produced when methane is burned.
Answer
Carbon monoxide is produced during the incomplete combustion of methane. This occurs when there is insufficient oxygen available for the reaction. In a limited oxygen environment, the methane (CH₄) does not fully oxidize, resulting in carbon monoxide (CO) being formed instead of carbon dioxide (CO₂). The overall reaction can be described as:
ightarrow ext{CO}(g) + ext{H}_2O(l)$$Step 3
Step 4
Calculate the volume of unreacted oxygen.
Answer
Using the balance of reactants:
- From the equation, the ratio of oxygen to carbon dioxide is 5:3.
- 3.60 dm³ of CO₂ requires:
ext{O}_2 ext{ needed} = rac{5}{3} imes 3.60 ext{ dm}^3 = 6.0 ext{ dm}^3
- Given the total oxygen used is 7.25 dm³:
- To convert this to cm³:
Thus, the volume of unreacted oxygen is 1250 cm³.