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AQA a-level chem unit 2 redox reactions - help

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    How do I know what to include and what not to include in half equations ? :confused:

    For example;

    (MnO4)^- + (Fe)^2+ + H^+ --> Mn^2+ + Fe^3+ + H2O

    Why is the half equation for the reduction;

    (MnO4)- + 5e --> Mn^2+

    and not;

    Mn^+7 + 5e- --> Mn^2+

    Someone please explain the concept to me of half equations in detail please.
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    That's not the half-equation for that reaction...it's not balanced. Half-equations need to be balanced in terms of particles and in terms of charge.

    It's not Mn7+ + 5e- ---> Mn2+ as Mn7+ as a species, does not exist in the full equation.

    The two half-equations are

    MnO4- + 8H+ + 5e- ---> Mn2+ + 4H2O
    Fe2+ ---> Fe3+ + e-

    Does that make sense?
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    (Original post by iAre Teh Lejend)
    How do I know what to include and what not to include in half equations ? :confused:

    For example;

    (MnO4)^- + (Fe)^2+ + H^+ --> Mn^2+ + Fe^3+ + H2O

    Why is the half equation for the reduction;

    (MnO4)- + 5e --> Mn^2+

    and not;

    Mn^+7 + 5e- --> Mn^2+

    Someone please explain the concept to me of half equations in detail please.
    You've confused me now! Your top two equations aren't balanced for oxygen or charge...:confused:
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    (Original post by dmccririck)
    You've confused me now! Your top two equations aren't balanced for oxygen or charge...:confused:
    Sorry bro, I meant to add the water and H+ ions where needed, but my question is about Mn so i forgot to add those.

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Updated: May 12, 2012
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