Redox Reactions - When and to include electrons?

Question

anonymous · Answer

For instance, if the half reactions were $$Zn ^{2+} + 2e ^{-} \rightarrow Fe$$
and $$Al ^{3+} + 3e ^{-} \rightarrow Al$$
I realise that you balance the reaction first, but what about the electrons.
DO you include them from the start on each side from the half reaction?
Or not use the ones in the half reaction, as in to just balance the charges?
So in a electrode potential question DeltaG=-nFE 
n would be 6 in this reaction?

aaronq · Answer

i'm guessing you meant Fe^2+ not Zn^2+.. 

but you have to balance the electrons first, thats essentially the most important part because electrons are being exchanged. 

whats the equation you're trying to balance?

anonymous · Answer

I think i understand it now, however stupid question is 2I and I2 the same? as if the charge was 2I- it would have an overall charge of -2 right?

aaronq · Answer

$$I _{2}$$ is a diatomic molecule of iodine with no charge/neutral, the oxidation state of I is 0.

$$2 I ^{-}$$

is two iodine anions each with an oxidation state of -1. 

they're not the same.

anonymous · Answer

two iodine anions each with an oxidation state of -1. , so overall 2I is charge 2- ?

aaronq · Answer

yeah, after you've balanced electrons, when you balance the charges you have to take those into account.