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A concentration cell built from a metal M is represented as: M(s) | M+(aq, 0.05 M) || M+(aq, 1 M) | M(s) The magnitude of the measured cell potential is |Ecell| = 70 mV. For this cell, which option is correct?
- Ecell < 0; deltaG > 0
- Ecell > 0; deltaG < 0
- Ecell < 0; deltaG(standard) > 0
- Ecell > 0; deltaG(standard) < 0
Correct answer: Ecell > 0; deltaG < 0
Solution
In a concentration cell the dilute side is the anode and the concentrated side is the cathode. The cell drives current spontaneously, so Ecell > 0. Since deltaG = -nF*Ecell, a positive Ecell means deltaG < 0. Note deltaG(standard) = 0 here because the standard cell potential of a concentration cell is zero (same electrodes), so options referencing deltaG(standard) are not the descriptor used.
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