Potential across a battery cell change ion concentrations and electron flow

[DumpmeAdrenaline]

I am trying to understand batteries and their electrochemical behavior

Consider a cell composed of two half cells where each half cell contains an electrode in an electrolyte solution. Different electrode materials have different tendencies to acquire or lose electrons. when the electrodes anode (ex. zinc electrode in ZnSO4 soln) and cathode (for ex. copper electrode in CuSO4 soln) are connected, electrons flow from the anode to the cathode to equalize the number of electrons and equilibrium is attained at which the voltage drops to 0.

The Nernst equation predicts that the cell potential is influenced by the concentration of active masses and the temperature.

E=1.10-(RT)(nF) * Log([Zn2+]/[Cu2+])

If potential is the work required to move an electron from an infinite distance to a point of interest.

When we apply an increasing time-varying potential across the cell will the concentration of [Cu(2+)] > [Zn2+]? If so, would this cause cause copper atoms on the electrode to dissociate and electrons to flow from the copper electrode to the zinc electrode?

Shouldn't the change in concentration of active mass be due to the redox reaction occurring at the electrode or does the potential applied across the cell imply only a stronger pull on the electrode with more electrons causing the electrode to become attracting anions surrounding the electrode towards it electrode?

 

[Borek]

If so, would this cause cause copper atoms on the electrode to dissociate and electrons to flow from the copper electrode to the zinc electrode?

If you apply external voltage then yes, you reverse the reaction. But it is not like "electrons flow from the copper electrode to zins electrode" - technically they do, but that's because we force them to do so.

Shouldn't the change in concentration of active mass be due to the redox reaction occurring at the electrode or does the potential applied across the cell imply only a stronger pull on the electrode with more electrons causing the electrode to become attracting anions surrounding the electrode towards it electrode?

Discharge is a spontaneous process going on its own, charging is nonspontaneous and requires external voltage. In both cases it is the same redox reaction, just the force behind is different. For the battery discharging is going with thermodynamics, discharging is going against thermodynamics (note: thermodynamics is not broken here, battery is a just a part of the system that is still following thermodynamics as a whole).

Kinda like a falling stone - when it falls, it is a spontaneous motion that just follows the gravity and the stone goes into the lowest energy position, when you bring it back up motion is "unnatural" and goes against the gravity (as long as you ignore whatever forces the stone to move).

 

[DumpmeAdrenaline]

If we consider the same cell under standard conditions and connect the two half cells through an external wire the standard cell potential would be 1.10 V. Electrons would flow spontaneously until the number of electrons is balanced.

The Nernst equation predicts that the cell potential is influenced by the concentration of active masses and the temperature and is described below for the following reaction.

E=1.10-(RT)(nF) * Log([Zn2+]/[Cu2+])

I am trying to understand what non-faradaic current is. If we connect the cell to a power source, that applies a potential across the cell that is greater than 1.10 V then according to Nernst equation electrode potential the zinc electrode surface would acquires a negative charge. I am confused between two points:

1) The equilibrium is disturbed, and to maintain a new equilibrium state, a reaction must decrease the number of electrons on the electrode surface to restore equilibrium.

2) The net charge on the electrode surface is negative so Zn2+ will diffuse from the bulk towards the electrode; Anions, on the other hand, will migrate away from the electrode. This migration of ions occurs until the electrode’s negative surface charge and the excess positive charge of the solution near the electrode's surface are balanced.

What dictates whether the zinc ions will acquire electrons to deposit as zinc atom or diffuse to balance the electrode's net charge?

Will the force on the electrons change due to the potential developed across the double layer formed across the zinc electrode-electrolyte interface affect (flow of ions I thought it meant electrons)? If so How?

 

[SredniVashtar]

I'd say it's the concentration of surface charge on the electrodes immersed in the solution.

 

[andrewb62]

If you are reversing the spontaneous reaction, the Zn electrode will be negative and Zn2+ cations will migrate towards the electrode. For the Cu electrode, it will be positive and so Cu2+ cations will be produced and migrate away from the electrode. Over the salt bridge, cations will move from the Cu/Cu2+ half cell to the Zn/Zn2+ half cell to maintain charge balance.