AQA GCSE · Question 05.3 · Chemistry of the atmosphere
Explain one negative impact on the environment of burning hydrogen rather than natural gas as a fuel. Use Table 2.
How to approach this question
1. Look at Table 2 again, this time looking for a negative impact.
2. Compare the amounts of the products for hydrogen and natural gas.
3. Identify a case where hydrogen is "worse" (produces more of a harmful substance).
4. State the harmful substance and explain *why* it is harmful to the environment.
Full Answer
While hydrogen combustion has the major benefit of not producing CO₂, it is not without environmental drawbacks.
- Looking at the row for "Mass of oxides of nitrogen produced", burning 1 dm³ of hydrogen produces 6.6 × 10⁻⁴ g, whereas natural gas produces 4.9 × 10⁻⁴ g.
- This means that, per volume of fuel, hydrogen combustion produces more NOx than natural gas combustion. This is often because hydrogen can burn at a higher temperature, which favours the reaction between nitrogen and oxygen from the air.
- Oxides of nitrogen are harmful pollutants. They can dissolve in water droplets in the atmosphere to form nitric acid, which then falls as acid rain. Acid rain damages buildings, harms aquatic life by acidifying lakes, and can kill trees. NOx can also contribute to the formation of smog and cause respiratory problems in humans.
Common mistakes
✗ Just stating "it produces more nitrogen oxides" without explaining the environmental consequence (acid rain, etc.).
✗ Choosing a substance where hydrogen is better (e.g., CO₂ or water).
✗ Misinterpreting the standard form numbers and thinking 4.9 × 10⁻⁴ is larger than 6.6 × 10⁻⁴.
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