Test 2 Q7


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Yea Eun Lee 1H
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Joined: Fri Sep 29, 2017 6:06 am

Test 2 Q7

Postby Yea Eun Lee 1H » Fri Mar 16, 2018 9:35 pm

Calculate the standard potential for the following reaction using the reduction potentials on the last page of the test: Fe3+ + 3e- ->Fe

I found two related half-reactions: Fe3+ + e- -> Fe2+ and Fe2+ + 2e- -> Fe
but I dont know what to do next. How do I solve this problem?

GabrielGarciaDiscussion1i
Posts: 71
Joined: Fri Sep 29, 2017 6:04 am
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Re: Test 2 Q7

Postby GabrielGarciaDiscussion1i » Sat Mar 17, 2018 1:34 am

If it's standard reduction potential, then couldn't you just combine the two standard reduction potentials since the Fe3+ would have to go through both reductions?
But then I also feel conflicted because I believe standard reduction potential is an intensive property and I believe intensive properties are not additive so, therefore that wouldn't work. However, I may be overthinking this and so I would ask Chem_Mod but I tried to supply whatever information I could. Sorry.

Tia Tomescu 2D
Posts: 42
Joined: Fri Sep 29, 2017 6:06 am

Re: Test 2 Q7

Postby Tia Tomescu 2D » Sat Mar 17, 2018 12:53 pm

I think you have to use deltaG=-nFE to calculate this.

Evelyn L 1H
Posts: 67
Joined: Fri Sep 29, 2017 6:05 am

Re: Test 2 Q7

Postby Evelyn L 1H » Sat Mar 17, 2018 1:14 pm

You have to use deltaG=-nFE because the number of moles of electrons are different in each equation.

After splitting up the given equation into the half reactions and finding Enaught, to find the standard potential of the reaction you would use
deltaG = -nFE

-nFE = -nFE + -nFE

-3FE= -1FE - 2FE -- cancel F

-3E = -1(0.77) - 2(-0.44) -- solve for E

-3E=0.11

E= -0.037V


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