iGCSE Chemistry (0620) Core:4.2 Hydrogen–oxygen fuel cells: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Statement 1 is correct: the overall reaction in a hydrogen-oxygen fuel cell is indeed $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$, producing water as the only chemical product. Statement 2 is incorrect because hydrogen does not come from the air—air contains very little hydrogen; the hydrogen must be manufactured or supplied separately. Statement 3 is also incorrect because the only waste product from a hydrogen-oxygen fuel cell is water, which does not cause respiratory problems. Therefore, only statement 1 is correct, making option B the right answer.
▶️ Answer/Explanation
Detailed solution:
In a hydrogen-oxygen fuel cell, hydrogen and oxygen are fed in and react cleanly to produce a flow of electrons (electricity), with water being the only chemical product. Option A is wrong because it makes hydrogen peroxide, $H_2O_2$. Option B is actually the reverse process, the electrolysis of water, which consumes electricity rather than producing it. The correct and balanced equation is $2H_2 + O_2 \rightarrow 2H_2O$, which is simply the reaction of hydrogen burning in oxygen, but carried out in a controlled way inside the fuel cell.
▶️ Answer/Explanation
Detailed solution:
A hydrogen-oxygen fuel cell works by reacting hydrogen and oxygen together electrochemically to produce electricity. The great thing about it is that the only chemical product is water ($\text{H}_2\text{O}$). There are no carbon emissions like carbon dioxide, and the original hydrogen and oxygen are reactants, not products.