Posted by **Keith** on Saturday, May 12, 2007 at 4:01pm.

I have an electrochem based question. I'm trying to solve for E* based on a chart in my book. I know the equation for solving this is E*= E*ox + E*red. The chart in my book gives a list of reactions and a E*red value. My teacher told us that the greater, or more positive, E*red value would remain the same and that half reaction would be the reduction, while the smaller E*red value's sign would be flipped along with it's equation to produce an oxidation. My question is this: if my book gives me a reaction that's backwards (ie: I want the reaction Fe+2 + 2e- --> Fe and the book gives me Fe --> Fe+2 + 2e-), would I switch the whole equation around, including the sign, before using the "more positive" rule to figure out the reduction reaction, or would I leave it as is, backwards, and use the rule based on those numbers?

Are you saying that the table values in your book are listed as oxidations (Fe==> Fe^+2+ 2e is an oxidation) or is the equation you show in the problem as an oxidation and the table values in the book are reduction values.

I just made up an equation on the spot to show that the equations in the book are the opposite of what I want. The table values are reduction.

OK. If the table values are all reductions then you make the decision by the rule as the reactions occur in the table. That rule is to tell you which equation is to be reversed and the sign changed. Then you make the reversal, change the sign, and add the E*ox + E*red for Ecell.

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