7.5 Hydrogen versus petrol as a fuel
5 exam questions worth 10 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is the only product when hydrogen burns in oxygen?
Choose one answer.
Correct Not quite: the answer is Water
Mark scheme
D
Model answer
D: 2H2 + O2 → 2H2O.
Give two advantages of using hydrogen instead of petrol as a fuel in cars.
Mark scheme
any two from:
- only product is water / no CO2 or pollutants (1)
- can be made from water, a renewable resource (1)
- releases more energy per kg (1)
Model answer
Burning hydrogen produces only water, so there is no carbon dioxide, and hydrogen can be made from water, which is renewable.
Give two disadvantages of using hydrogen as a fuel in cars.
Mark scheme
any two from:
- difficult to store / needs high pressure tanks (1)
- explosive / highly flammable (1)
- energy needed to produce it, often from fossil fuels (1)
- few refuelling stations (1)
Model answer
Hydrogen is hard to store because it is a gas, and it is explosive.
A newspaper says that hydrogen cars produce no carbon dioxide. Evaluate this claim.
Mark scheme
- true at the point of use: the only product is water (1)
- but hydrogen is often made from natural gas, releasing CO2 (1)
- or by electrolysis using electricity that may come from fossil fuels (1)
Model answer
At the car itself, only water is produced, so the claim is true there. However, most hydrogen is made from natural gas, which releases carbon dioxide, or by electrolysis using electricity that may come from burning fossil fuels, so carbon dioxide may still be released overall.
Name two pollutants, other than carbon dioxide, produced by petrol cars.
Mark scheme
any two from:
- carbon monoxide (1)
- soot / carbon particulates (1)
- nitrogen oxides (1)
- unburnt hydrocarbons (1)
Model answer
Carbon monoxide and nitrogen oxides.
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