## calculating standard cell potential

hannahdaijo_4H
Posts: 48
Joined: Fri Sep 28, 2018 12:27 am

### calculating standard cell potential

Why is standard cell potential sometimes equal to the difference between the standard potentials of the two electrodes and sometimes its the sum of the standard potentials of the cathode and the anodes?

AnnaYan_1l
Posts: 96
Joined: Fri Apr 06, 2018 11:05 am
Been upvoted: 1 time

### Re: calculating standard cell potential

Half reactions are usually given as reduction reactions.

It's the difference when you're keeping both anode and cathode 's at their reduction potentials

It's added when you flip the anode reaction (making it go from a reduction to oxidation) and thus flip .

Hope that helps!

Kassidy Tran 1E
Posts: 77
Joined: Fri Sep 28, 2018 12:15 am

### Re: calculating standard cell potential

There are two ways of calculating standard potential (E). You can either use E_cell = E_cathode - E_anode, in which you just take the standard reduction potentials from the chart and plug them into the equation as is, without changing the signs, or you can add up the half reactions and their standard potentials. In the second method, you would have to flip the anode so that the electrons cancel out, and because you flipped the reaction, you need to flip the sign of the standard reduction potential. In this case you would just add the two E values together as you do with the half reaction equations.

1K Kevin
Posts: 47
Joined: Fri Sep 28, 2018 12:24 am

### Re: calculating standard cell potential

YES this finally made sense to me now thank thank you so much! i could never tell when to flip or not thank you!

SydBenedict2H
Posts: 60
Joined: Wed Nov 08, 2017 3:00 am

### Re: calculating standard cell potential

Just remember that if you use the overall net equation for E you leave the signs and if you're adding up form had reactions etc. you have already flipped the sign so just add.

ryanhon2H
Posts: 60
Joined: Fri Sep 28, 2018 12:28 am

### Re: calculating standard cell potential

If you subtract cathode - anode, you don't flip the signs. If you add them, then you would have to flip the sign of the anode.