Where do electrons flow inside a battery? What happens inside a battery?

Question

Sorry, if this sounds silly, but I have had this doubt from a long time. Please help me, I'll forever be grateful to you. I'm a student of 10th grade. This is my doubt:

• What happens when electrons from the negative terminal reaches the positive terminal through the wire?
• After they reach the positive terminal, what happens to them?
• Do those same electrons again start flowing inside the battery, to the negative terminal of the battery, through the wire, then again to the positive terminal?
• Or, the chemical reactions inside the battery produce new electrons which go to the negative terminal of the battery, then start flowing through the wire?

When the electrons keep flowing to the positive terminal,the electrons should be equal at the positive plate as it is in the negative plate, basically, equilibrium should be reached, then at that time,the electron flow should stop, so the battery should finish.

• Then why does the battery not finish then, rather it finishes when the chemicals inside the battery become useless?

I'm a 10th grader and I have tried to find answers from everywhere but I am not satisfied and there are mixed answers, some contradicting the other, so please give the valid answer and try to explain it as simply as you can. Thanks a lot.

Answer 1

$\require{mhchem}$Electrons flow inside galvanic cells(*) only along the wiring and conductive electrodes. They are released and captured at boundaries of electrodes and an electrolyte.

Let consider the classical Leclanché cell, based on $\ce{Zn|NH4Cl|MnO2}$ schema:

At the anode ( the more negative pin where oxidation occurs ), there is ongoing reaction pushing released electrons to the wire.:

$$\ce{Zn(s) -> Zn^2+(aq) + 2e-}$$

At the cathode ( the more positive pin where reduction occurs ), there is ongoing reaction attracting electrons from the wire:

$$\ce{2 MnO2(s) + 2 NH4+(aq) + 2e- -> Mn2O3(s) + 2 NH3(aq) + H2O(l)}$$

So the electrons are released free on the anode and bound again on the cathode.

Such processes cause a very slight charge dis-balance, with a very slight excess of positive charge at the anode and a similar lack of positive charge at the cathode. This causes induced potential gradient leading to electromigration of positive and negative ions to cancel such a gradient.

The overall chemical reactions, copied from the Wikipedia article for convenience, are:

$$\ce{Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) -> ZnCl2(aq) + Mn2O3(s) + 2 NH3(aq) + H2O(l)}$$ or if one also considers the hydration of the $\ce{Mn2O3(s)}$ sesquioxide into $\ce{Mn^{III}}$ oxy-hydroxide: $$\ce{Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) -> ZnCl2(aq) + 2 MnO(OH)(s) + 2 NH3(aq)}$$ Alternately, the reduction reaction of $\ce{Mn^{IV}}$ can proceed further, forming $\ce{Mn^{II}}$ hydroxide. $$\ce{Zn(s) + MnO2(s) + 2 NH4Cl(aq) -> ZnCl2(aq) + Mn(OH)2(s) + 2 NH3(aq)}$$

For more, follow the multiple search hits e.g. here: Google site:libretexts.org galvanic cell on the site, dedicated to education.

---

(*) The commonly used term "battery" is misused. As the original meaning of a battery is a kind of spatially organized set of items. These items may be galvanic cells ― like a car battery of 6 or 12 acid lead galvanic cells ― or also artillery cannons.

Answer 2

If you have no external connections to a battery then due to the electro-chemical reaction inside the battery electrons move from the positive terminal (making it more positive) to the the negative terminal (making it more negative).

This creates an electric field within the battery from the positive terminal to the negative terminal and this electric field opposes the movement of electrons from the positive terminal to the negative terminal.

Eventually the electric field is strong enough to stop the net movement of electrons from the positive terminal to the negative terminal.
So you now have a battery with a positive terminal (deficit of electrons) and a negative terminal (surplus of electrons) with a potential difference across them.

Answer 3

We can understand a battery as a type of controlled corrosion. When a carbon steel bolt for example is attached to a brass nut in a humid environment, the bolt corrodes with time, as positive ions of iron migrate spontaneously to the nut. The lost electrons also move from the bolt to the nut because they are in close electric metal contact.

In a battery, very schematically, 2 metals are joined in a corrosive environment, but in such a way that there is no metal-metal contact. So the only way for the chemical corrosion reaction to complete is joining them outside by a wire. The electrons move to balance the metal charges, due to the migration of the positive ions.

So, it is not that the electrons are moving in a loop through the circuit. They are moving from pole A to pole B by outside, while ions are also moving from A to B, but inside. Pole A loses material (ions and electrons) to the other. After some time, the corrosion is too advanced and the battery is discharged.