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Chemistry Question: No of Moles of Electrons transferred

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  • 13-03-2012 6:36pm
    #1
    ericm84
    Registered Users Posts: 20 ✭


    Hi Guys,

    From a non-chem background and studying for the Gamsat for Grad Medicine entry. Going over past papers and there is a question that I have come across that I can't for the life of me figure out. I'll post it below:

    If Eocell and Keq at 25OC are related by: Eocell = 0.06/nlog10Keq
    Where n is the number of moles of electrons transferred in the reaction, what is the value of Keq for the following reaction:


    CH3CH2OH + (1/2)O2 -> CH3CHO+H2O (E0 = 1.02V)
    A. 17.0
    B. 34.0
    C. 1.0 X 1017
    D. 1.0 X 1034

    The answer is D and the explanation is fairly simple, just plug all the numbers into the formula and there you go, fair enough.

    My problem is n..........in the answer sheet they say that this is 2 because there are 2 moles of electrons transferred in the reacation.
    How do you know that there are 2 moles of electrons transferred???
    I'm stumped (and also a little embarassed that I dont know the answer as I'm sure its easy:o!!)

    Thanks in advance!


Comments

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    #2
    Parsley
    Closed Accounts Posts: 3,144 ✭✭✭Parsley


    well, you take 2 hydrogens from the ethanol to transfer to the oxygen. one electron goes with each hydrogen, or one mole of electrons per mole of hydrogen.


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    #3
    ericm84
    Registered Users Posts: 20 ✭ericm84


    Ahh....ok I see it now (knew it was something obvious!!). Thanks very much for that. I think I was trying to over complicate it by trying to calculate oxidation numbers in the redox reaction and getting myself all mixed up!!


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    #4
    Parsley
    Closed Accounts Posts: 3,144 ✭✭✭Parsley


    ericm84 wrote: »
    Ahh....ok I see it now (knew it was something obvious!!). Thanks very much for that. I think I was trying to over complicate it by trying to calculate oxidation numbers in the redox reaction and getting myself all mixed up!!

    well you can do it that way too. the oxygen goes from 0 to -2. => two moles of electrons. :)


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