How Do You Calculate Cell Potentials for Electrochemical Couples?

[w3390]

Homework Statement

Calculate the potential of a Zn^2+/Zn and Ag^1+/Ag couple.

Homework Equations

Zn^2+ + 2e^1– ⇌ Zn E= –0.76 V
Ag^1+ + e^1– ⇌ Ag E= +0.80 V

The Attempt at a Solution

First I know to multiply the silver half reaction by two so that each half reaction has two electrons. Then I flip the zinc reaction and switch the sign of its energy. Then, I added the two energies to get a cell potential of 1.56V. However, my homework is telling me that this is incorrect. I can not think of any reason why that is so. Any suggestions? Any help would be much appreciated.

 

[Borek]

E is not energy. You don't need to balance reaction to calculate potential. You don't flip the reaction - direction doesn't matter, both oxidation and reduction are both taking place at exactly the same potential.

All that being said, 1.56 looks fine to me... I can be missing something - it happens, especiall early in the morning - but I think it is OK.

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[Blueshift5]

Your approach to calculating the cell potential is correct. However, the homework statement may have a typo as the correct cell potential for the Zn^2+/Zn and Ag^1+/Ag couple is 1.56 V. It is possible that the homework meant to ask for the potential of a Zn/Zn^2+ and Ag/Ag^1+ couple, in which case the correct cell potential would be -1.56 V. It is always important to double check the information given in the homework statement and equations to ensure accuracy in calculations.