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Q & A: Which way do the electrons flow in a battery.

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Q:
Do electrons flow from the positive end of a battery to the negative end (via a simple series circuit) or from the negative end to the positive?
- Mike
Pocatello,Id
A:
Electrons are negatively charged, and so are attracted to the positive end of a battery and repelled by the negative end. So when the battery is hooked up to something that lets the electrons flow through it, they flow from negative to positive.

You might wonder why the electrons don't just flow back through the battery, until the charge changes enough to make the voltage zero. The reason is that an electron can't move from one side to the other inside the battery without a chemical reaction occurring. In other words, inside the battery plain electrons can’t travel around because it takes too much energy to put a plain electron in solution. Electrons can only travel inside the battery via charged chemicals, ions, which can dissolve off the electrodes. The chemical reaction is what pushes the electrons inside toward the negative end, because the electrodes at the two ends are made of different materials, which have different chemical stabilities. So overall, electrons flow AROUND the circuit, toward the negative end inside the battery, pushed by the chemical reaction, and toward the positive end in the outside circuit, pushed by the electrical voltage.

Electrical current can flow in the other way in the battery too, if the battery is hooked up to something with a bigger voltage difference (a battery charger, for example).

Tom (and Mike)

(republished on 07/13/06)

Follow-Up #1: Battery chemistry followup

Q:
How chemical reaction in a battery pushes the charge to flow in a circuit?
- shahzad
pakistan
A:
good question- we’ve modified the answer above to try to incorporate at least a little of the answer in it.

Mike W

(published on 01/10/07)

Follow-Up #2: how do electrons act?

Q:
Hello. I would have 3 questions: 1. The electrons generated in one type of electrolyte (A) push those in the conductor (like cars bumper-to-bumper) when the circuit is closed and thus start traveling from one electrode to the other. Now, when they get from that electrolyte A through the conductor reaching the destination electrode, DO THOSE ELECTRONS ENTER ELECTROLYTE BY JOINING THE IONS OR DO THEY JUST RESIDE ON THE ELECTRODE ITSELF? as to the electrolytes, I am referring to http://en.wikipedia.org/wiki/Galvanic_cell 2. The electrons possess energy - they spin. It is kind of a crazy jumping all around the place within the atom - it almost seems that they are each time in many places. The question: where the hell they get that energy for it (Big Bang?)? Do they lose that energy over time? - do they get exhausted? 3. Are there different types of electrons - in respect to their content?
- Martin
A:
That's a challenging, diverse set of questions.

1. The electrons in the particular galvanic cell you mention join up with Cu++ ions from the solution to make plain Cu atoms, which sit on the Cu electrode.

2. Electrons, like all small things, are indeed fuzzed-out waves, not located in one exact place.  The picture of them always hopping around, as if they were first somewhere then somewhere else, is not correct for electrons that have settled in to wave patterns in atoms. However, (and this should admittedly sound strange before you learn a little quantum mechanics) even in those stable patterns the electrons have some kinetic energy. More importantly, whether classical or quantum, energy is conserved. It doesn't disappear. The large-scale organized forms of it gradually trickle away into smaller-scale forms, allowing a great diversity of possible states. (That's the implication of second law of thermodynamics.)  Anyway, all this energy has been around since the Big Bang, as you supposed.

The electron spin is something else, a part of what makes something an electron, and it persists undiminished unless the electron is annihilated.

3. No, electrons are really all the same sort of thing. That's not just a philosophical statement. Electrons are a type of particle called "fermions", for which no two identical particles can have exactly  the same quantum state. If you pick some spatial wave pattern, it can only have two electrons in it- one for each distinct spin state. That has enormous consequences. For example, it's the only reason that all the electrons in an atom don't pile up in a boring low-energy ball near the nucleus, so it accounts for all of chemistry and hence life.

Mike W.

(published on 05/07/11)

Follow-Up #3: electrons in a battery

Q:
Hi there, I was wondering, is there an electron flow inside the actual cell itself once it is connected to a charger to charge the battery?? im talking about inside the cell itself because there is nothing on the net that comes up with the level answer i was looking for. Thanks
- Sohail (age 23)
Australia
A:
There's essentially no flow of individual free electrons inside the battery. However, there is a net flow of electrons since the ions include electrons. For example. consider a Cu electrode. As the battery is charged, electrons flow in from the charger and Cu++ ions flow in from solution. Since those ions still have electrons in them, there is electron flow. Likewise whatever negative ions flow toward the other electrode also carry electrons. There's no rule requiring that those two electron flows cancel.

Mike W.

(published on 07/18/12)

Follow-Up #4: electrons in battery fluid?

Q:
I am still thinking why electrons can't flow through electrolyte? In case of lithium ion battery it is clear that electrolyte consists of organic liquid which is insulator to electricity but conductor for ions but batteries like Lead acid battery has water and sulphuric acid in electrolyte compartment. Why electrons can't flow through this electrolyte and short circuit the battery?
- Shoaib (age 26)
Korea
A:
Really the H2O-H2SO4 solution is quite similar to the liquid in other batteries, in that individual electrons are almost insoluble in it. It's far easier for ions to flow in it, and for electrons to flow through the rest of the electrical circuit.

Mike W.

(published on 08/02/12)

Follow-up on this answer.