Electrolytic/Galvanic cells help!

[Atl21]

Cd2+ + 2e- = Cd = -.40
Ag1+ + 1e- = Ag = .80


What is the standard cell potential for the spontaneous reaction that would occur involving cadmium and silver and their respective ions? How can i do this problem? Thanks all

 

[jdx915]

I think you just take the reduction half (which is always the larger number) and subtract the oxidation half. So you would do .80-(-.40) which would give 1.2. Correct me if im wrong

 

[TheRxQueen]

If the reaction is spontaneous, right away you know it's a Galvanic cell and the Ecell (standard cell potential) has to be positive.
Ecell = (cathode) - (anode)
Reduction occurs at the cathode; Oxidation occurs at the anode
(to remember these associations, I was taught CaR and AutO)

The silver is the species most easily reduced (because it has the most positive value), so I would say that one occurs at the cathode.

Calculating standard cell potentials isn't affected by the number of electrons or stoichiometric coefficients of the net equation, so....

Just plug in the numbers: Ecell = (0.80) - (-.40) = 0.8 + 0.4 = 1.2 V

If you had plugged in the numbers backwards, the result would have been a negative number(-0.4 - 0.8), which doesn't equate to a spontaneous reaction so that would be the red flag that your answer is wrong.

Does this help?

 

[Atl21]

Thanks guys, but what if the equation is nonspontaneous?

 

[Atl21]

Would the answer be -1.2V? It seems like negative value in electrolyic cell is nonspontaneous, but in Gibbs free energy, negative value is spontaneous. Am i correct, please correct me if i am wrong. Thanks

 

[nerv12345]

^you are correct