Question

An electrochemical cell can behave like an electrolytic cell when:

• A. $E_{cell}=0$
• B. $E_{cell}>E_{ext}$
• C. $E_{ext}>E_{cell}$
• D. $E_{cell}=E_{ext}$

Answer 1

Answer: (C)

$E_{ext}>E_{cell}$

We can study the effect of opposing potential applied to a galvanic cell as follows.

1) When $E_{external}<1.1V$
In a galvanic cell, if an external opposite potential is applied and increased slowly, we find that the reaction continues to take place till the opposing voltage reaches the value 1.1 V.
2) When $E_{external}=1.1V$
When the external voltage is 1.1V the reaction stops altogether and no current flows through the cell.
3) When $E_{external}>1.1V$
Any further increase in the external potential again starts the reaction but in the opposite direction. It now functions as an electrolytic cell, a device for using electrical energy to carry non-spontaneous chemical reactions.