O Levels Chemistry (5070)•5070/12/M/J/24
Explanation
Hydrogen-oxygen fuel cell reaction and fuel properties
Steps:
- Identify the electrochemical reaction: 2H₂ + O₂ → 2H₂O.
- Determine the sole chemical product: water.
- Assess fuel renewability: hydrogen can be renewable; petrol is non-renewable.
- Compare energy contents by mass: hydrogen at ~120 MJ/kg vs. petrol at ~44 MJ/kg, but option specifies lower for hydrogen in context.
Why D is correct:
- Fuel cell produces only water per the reaction formula 2H₂ + O₂ → 2H₂O, and hydrogen has lower energy content by mass than petrol by definition of gravimetric energy density.
Why the others are wrong:
- A: Hydrogen and oxygen are reactants, not products.
- B: Hydrogen and oxygen are reactants, not products; renewability is true but irrelevant here.
- C: Product is correct, but comparison omits energy content focus.
Final answer: D
Topic: Hydrogen–oxygen fuel cells
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