A hydrogen and oxygen fuel cell delivers a steady 7.5 A at 0.62 V for 3.0 hours…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A hydrogen and oxygen fuel cell delivers a steady at for hours. The anode reaction is . Burning one mole of hydrogen would release as heat. Find the moles of hydrogen used, the electrical energy delivered in kilojoules, and the efficiency as a percentage of the heat that burning that hydrogen would give.
Need a reminder? The key ideaShow
One ampere-hour is . A lead atom gives 2 electrons in the lead storage battery, a zinc atom gives 2 in the dry cell and an iron atom gives 2 when it rusts. Energy is . A fuel cell converts the energy of directly into electricity. Zinc, with a lower potential than iron, protects it.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Charge. .
Step 2. Hydrogen. Electrons: . Each gives 2, so of hydrogen.
Step 3. Energy delivered. .
Step 4. Energy in the fuel. .
Step 5. Efficiency. .
Answer: of hydrogen, of electrical energy and an efficiency of .
Check. The best possible is about , set by . A cell delivering current at a voltage below its emf of is well below that.
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