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OCR F325 A2 Chemistry Fuel Cells

I'm so confused about what we're supposed to know about hydrogen fuel cells. I have two textbooks and one of them quotes the half equations for an alkaline electrolyte:
H2 + 2 OH- => 2H2O + 2e-
1/2 O2 + H2O + 2e- => 2 OH-
And one gives the half equations for an acid electrolyte:
H2 => 2 H+ +2 e-
1/2 O2 +2 H + 2 e- => H2O
To me the equations for an acid electrolyte make much more sense in terms of what is actually going on; I don't get the ones with an alkaline electrode at all. The spec just says 'Explain the changes that take place at each electrode in a hydrogen-oxygen fuel cell' so I'm so confused about which ones to learn as the two textbooks conflict. If anyone can help thank you so much in advance!
Sorry you've not had any responses about this. :frown: Are you sure you've posted in the right place? :smile: Here's a link to our subject forum which should help get you more responses if you post there. :redface:

You can also find the Exam Thread list for A-levels here and GCSE here. :dumbells:


Just quoting in Puddles the Monkey so she can move the thread if needed :h:

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Reply 2
Avatar for Miminfl
Miminfl
6
This explains it pretty well, https://youtu.be/xDBNJpcoGrk
If you don't find it go to machemguy on YouTube and go to his playlist go to unit f325 energy which will include a video on fuel cells.
Reply 3
Avatar for Pigster
Pigster
20
It is easy to convert any acid half equation into an alkaline one:

Add as many OH- to both sides are there are H+. Convert the H+ and OH- to water. Cancel the waters from both sides (as required).

e.g. MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O
becomes
MnO4- + 8H+ +8OH- + 5e- -> Mn2+ + 4H2O + 8OH-
becomes
MnO4- + 8H2O + 5e- -> Mn2+ + 4H2O + 8OH-
becomes
MnO4- + 4H2O + 5e- -> Mn2+ + 8OH-

Applying that to fuel cells:

H2 -> 2H+ + 2e-
becomes
H2 + 2OH- -> 2H2O + 2e-

O2 + 4H+ + 4e- -> 2H2O
becomes
O2 + 2H2O + 4e- -> 4OH-
Reply 4
Avatar for medics_r_us
medics_r_us
OP
1
Original post by Pigster
It is easy to convert any acid half equation into an alkaline one:

Add as many OH- to both sides are there are H+. Convert the H+ and OH- to water. Cancel the waters from both sides (as required).

Thank you so much for this!

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