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To determine if a redox
reaction is spontaneous,
you should compute the
voltage of the reaction.
- If the voltage is positive, the reaction is spontaneous
- If the voltage is negative, the reaction is not spontaneous
Example: Is the reaction below spontaneous?
- Cu(s) + 2Fe+3(aq) -> Cu+2(aq) +
2Fe+2(aq)
Solution: To determine spontaneity, we need to determine the voltage.
Break the reaction up into two half reactions and check the voltages of each
- Cu(s) -> Cu+2 + 2e- Eox =
-0.339 V
- Fe+3(aq) +e- -> Fe+2(aq)
Eox = +0.769 V
The cell voltage is thus E = Ered
+ Eox = -0.339 + 0.769 = +0.43 V. Since E is positive, the
reaction is spontaneous. |