- #1
Comeback City
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I created a simple battery. I used a copper cathode and zinc anode resting in a saturated solution of NaCl (about 25% NaCl by mass), connected by alligator clips to a voltmeter. I received a voltage of .85V, whereas the theoretical voltage should have been about 1.10V. That's not of too much concern, considering my setup wasn't top-notch by any means, and the voltmeter I used is rather old.
I attempted to find the half-reactions of this scenario, in which the full redox is...
Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu (s)
I found the half reactions to be...
Zn(s) -> Zn2+(aq) + 2e-
Cu2+(aq) + 2e- -> Cu(s)
These half-reactions had to be arranged in such a way as to combine to form the full redox. This can be explained by activity series, where Zn is more easily oxidized than Cu. This leaves the Zn half-reaction as the oxidation and Cu as the reduction.
My question... can the determination of which half-reaction is to be an oxidation or reduction be explained through the spontaneity of the reaction as well? I went through, using the formula...
ΔG = ΔH - TΔS
...and found the change in free energy to be approximately -211 kJ, which I also confirmed using ΔG = -nFE. Thus, the redox is spontaneous and should occur on its own, as it did in the battery. If my logic is correct, would that also imply that free energy and spontaneity generally explains the activity series? For example, Li is higher than Zn on the activity series, and has a much lower ΔG than Zn. Zn is higher than Cu on the series, and has a much lower ΔG than Cu.
Thank you in advance!
I attempted to find the half-reactions of this scenario, in which the full redox is...
Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu (s)
I found the half reactions to be...
Zn(s) -> Zn2+(aq) + 2e-
Cu2+(aq) + 2e- -> Cu(s)
These half-reactions had to be arranged in such a way as to combine to form the full redox. This can be explained by activity series, where Zn is more easily oxidized than Cu. This leaves the Zn half-reaction as the oxidation and Cu as the reduction.
My question... can the determination of which half-reaction is to be an oxidation or reduction be explained through the spontaneity of the reaction as well? I went through, using the formula...
ΔG = ΔH - TΔS
...and found the change in free energy to be approximately -211 kJ, which I also confirmed using ΔG = -nFE. Thus, the redox is spontaneous and should occur on its own, as it did in the battery. If my logic is correct, would that also imply that free energy and spontaneity generally explains the activity series? For example, Li is higher than Zn on the activity series, and has a much lower ΔG than Zn. Zn is higher than Cu on the series, and has a much lower ΔG than Cu.
Thank you in advance!