I have a table of standard potentials in water that gives a number of reactions and their e*reduction. Say I'm looking for the reaction Al(s) -- Al+3 + 3e-, but the book gives me the reaction Al+3 + 3e- -- Al(s) and a E*red value of -1.68. If this were to react with something else, would I first flip the second equation, including the sign, so I have it going in the correct direction, and THEN possibly flip it back if I find that this reaction is actually the oxidation half reaction?

Question

I have a table of standard potentials in water that gives a number of reactions and their e*reduction. Say I'm looking for the reaction Al(s) --> Al+3 + 3e-, but the book gives me the reaction Al+3 + 3e- --> Al(s) and a E*red value of -1.68. If this were to react with something else, would I first flip the second equation, including the sign, so I have it going in the correct direction, and THEN possibly flip it back if I find that this reaction is actually the oxidation half reaction?

I hope this made sense. Our teacher told us that when you have two half-reactions, the one with the more positive E*red will be the reduction half reaction, and the sign of the other half reaction is switched to make it an oxidation. My question is, do you still do the flipping if you have to flip the sign of the oxidation reaction anyway to make it go the right way?

Yes, the reverse reaction will occur if a more electronegative reduction is the other half reaction.

Yes, the reverse reaction will occur if a more electronegative reduction is the other half reaction.