# Homework Help: Finding voltage through values in an appendix

1. May 5, 2013

### silenzer

1. The problem statement, all variables and given/known data

Find the Ered° values in the appendix for the cathode and anode in the reaction

3Ce4+(aq) + Bi(s) + H2O(l) → 3Ce3+(aq) + BiO+(aq) + 2H+(aq)

2. Relevant equations

None.

3. The attempt at a solution

So in my appendix there is a value for the Ce4+/Ce3+ half-reaction, but only the reverse reaction for Bi(s) + H2O(l) → BiO+(aq) + 2H+(aq). What do you do then?

Last edited: May 5, 2013
2. May 6, 2013

### Staff: Mentor

Hi silenzer. I'd guess that you simply take the negative of that voltage. But it's a long time since I did any chem. My recommended approach is to do a web search for a similar worked example to see whether that's the way. I'd be surprised if your text book didn't have a worked example.

Of course, if you know the correct answer for your question, you can work it out and compare to see whether my guess is right.

3. May 6, 2013

### Staff: Mentor

While tables of standard potentials are often called "reduction potential tables", and reactions are written as reduction, it is just a matter of convention (makes it easier to find what you are looking for). Reaction goes both ways at a given potential. Or more precisely, when you mix all substances in their standard states (1 bar, 1M), and you put an inert electrode into the solution, you will read the standard potential as given. Whether the observed reaction will be reduction or oxidation will depend solely on the second half cell.

In other words - no need to flip the sign, cell voltage is just a matter of distance between standard potentials, regardless of whether they are given as reduction or oxidation.