What happens when an opposing external potential (Vext) equal to 1.10 V is applied across a standard Daniell cell (Zn | Zn2+(1M) || Cu2+(1M) | Cu)?
Answer and explanation
Correct answer: D. The net cell reaction ceases completely, no electrons flow, and current drops to zero
- When , electrons continue to flow from to (galvanic action);
- When , the external potential exactly balances the cell EMF, no chemical reaction occurs, and current becomes zero;
- When , the process reverses, driving an electrolytic cell where electrons flow from to .
- When , the external potential exactly balances the cell EMF, no chemical reaction occurs, and current becomes zero;
- When , the process reverses, driving an electrolytic cell where electrons flow from to .
- Step 1: The standard electromotive force of a Daniell cell is .
- Step 2: If an opposing external voltage is applied:
Answer
The net cell reaction ceases completely, no electrons flow, and current drops to zero
Why not the others: 'Electrons flow from zinc to copper at twice the rate' is impossible because opposing voltage counteracts current; 'The cell operates as an electrolytic cell...' occurs only when ; 'Zinc precipitates rapidly...' occurs only during reverse electrolysis.
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