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AQA a-level chem unit 2 redox reactions - help

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1. How do I know what to include and what not to include in half equations ?

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.
2. 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?
3. (Original post by iAre Teh Lejend)
How do I know what to include and what not to include in half equations ?

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...
4. (Original post by dmccririck)
You've confused me now! Your top two equations aren't balanced for oxygen or charge...
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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