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Having an issue calculating the standard cell potential?
I know the equation is E=Ecathode-Eanode, but I struggle with the fact that it is E=Ered+Eoxi. Why is there a sign change in the equation? I'm confused because reduction occurs at the cathode and oxidation at the anode, so I would think the two equations would be the same.
Thanks!
1 Answer
- pisgahchemistLv 77 years ago
Consider an example where zinc metal is added to a solution of copper(II) ions.
"A red cat ate an ox." ..... Reduction occurs at the cathode (red cat), oxidation occurs at the anode (an ox).
Zn --> Zn2+ + 2e- ........................ E = +0.76V ...... oxidation (anode)
Cu2+ + 2e- --> Cu(s) ................... E = +0.34V ...... reduction (cathode)
-------------------- ------------------- --------------------
Zn(s) + Cu2+ --> Zn2+ + Cu(s) ... E = +1.10V .... E = E(red) + E(oxi)
In the first equation....
E = E cathode - E anode
the reduction potential is used for both.
E = (+0.34V) - (-0.76V) = +1.10V
