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I was wondering if someone would help me with my question. I was completing a question which asked about the effect of increased surface area of a platinum electrode on the EMF of the overall cell.

This is the cell: Pt | H2O2(aq), O2(g) || IO (aq), I2(aq) |Pt

When I answered, I thought the EMF would increase due to the surface area of the electrode being able to now accept more electrons but I found out the answer is that the EMF is unaffected by any change in surface area, why is this?

Thanks for any help anyone can provide!

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  • $\begingroup$ This is the same difference as between voltage and current. A bigger surface should increase the current. $\endgroup$ – TAR86 May 9 '17 at 10:12
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If by EMF you mean the ideal, thermodynamically determined, voltage then the answer is that increasing the surface area does not affect voltage/EMF. If by EMF/Voltage, the questions means operational voltage then it will increase because increasing the surface area of electrodes decreases the overpotential losses (Tafel equation) by essentially decreasing the resistance due to the kinetics of the reaction thus increasing operational/real voltage of a cell.

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When electrode surface area increases,internal resistance decreases.But emf does not change as it is a characteristic of a cell.Emf only depend upon nature of electrodes and electrolyte.

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