Do electrons flow through a battery or is it something else?

[vcsharp2003]

Homework Statement

In a closed circuit as shown in diagram below, a current is flowing i.e. electrons are flowing in a direction opposite to conventional current direction. What happens to the flowing electrons when they reach the positive terminal of the battery?

Relevant Equations

None

This is a confusing question. I am not sure if electrons flow through the battery from positive terminal to negative terminal against the electric field within the battery; or the electrons deposit on positive plate resulting in a chemical reaction that releases electrons at the negative plate which supplies free electrons to flow away from negative terminal in circuit.

 

[phinds]

What research have you done on this so far? What have you found?

 

[vcsharp2003]

What research have you done on this so far? What have you found?

I have looked up my course book, and it doesn't explain. It says that some work is done in moving a -ve charge within the battery implying that electrons flow through the battery , but it doesn't explicitly say that electrons flow through a battery.

 

[phinds]

Well, your book is a good place to start. Can you think of any other readily available resource that you might tap into?

 

[vcsharp2003]

Well, your book is a good place to start. Can you think of any other readily available resource that you might tap into?

I have tried Google search but it didn't yield anything useful.
If this is not a valid question for Physics forums, then I guess it needs to be deleted.

 

[Delta2]

I find this a very interesting question for anyone who is interested in the internal workings of a battery. I am not sure at all here, but I think you second explanation (electrons don't really flow but a chemical reaction happens) seems more plausible to me.

 

[phinds]

I have tried Google search but it didn't yield anything useful.

I find that astounding since I found the answer on the first go.

 

[vcsharp2003]

I find this a very interesting question for anyone who is interested in the internal workings of a battery. I am not sure at all here, but I think you second explanation (electrons don't really flow but a chemical reaction happens) seems more plausible to me.

I really appreciate your honest answer and thanks for helping me. It appears to me too since a battery has an electrolyte between it's terminals in which a chemical reaction occurs, probably resulting in electron capture by atoms of electrolyte.

 

[vcsharp2003]

I find that astounding since I found the answer on the first go.

I found this https://www.science.org.au/curious/...text=A battery is a device,be used to do work. but it also appears to say that electrons flow from one end to the other.

 

[Tom.G]

The 'Go To' place for all things battery is:
https://batteryuniversity.com/

Enjoy!
Tom

 

[Delta2]

Actually on second thought I *think* I 've found the answer myself. And yes the answer is that electrons (or positive ions) flow inside the battery regardless of what chemical reactions might happen.

To reach to this answer, think about conservation of charge on each of battery's terminals.

 

[vcsharp2003]

Actually on second thought I *think* I 've found the answer myself. And yes the answer is that electrons (or positive ions) flow inside the battery regardless of what chemical reactions might happen.

To reach to this answer, think about conservation of charge on each of battery's terminals.

You mean, if electrons are available on negative terminal due to whatever reason, then the positive terminal must become equally positively charged i.e. it must have lost electrons as electrons can neither be created or destroyed. But, the electrolyte between the electrodes also participates in conservation of charges, so how do we explain the electrolyte having a net zero charge if the previous statement is correct.

 

[Delta2]

You mean, if electrons are available on negative terminal due to whatever reason, then the positive terminal must become equally positively charged i.e. it must have lost electrons as electrons can neither be created or destroyed. But, the electrolyte between the electrodes also participates in conservation of charges, so how do we explain the electrolyte having a net zero charge if the previous statement is correct.

As you said, electrons reach the positive terminal due to the current in the rest of circuit. If these electrons didn't flow -through the electrolyte - to the negative terminal then the charge of the positive terminal would become zero or negative after sometime. Similarly for the negative terminal if it would keep releasing electrons to the rest of circuit, it would become zero charged or positively charged unless of course electrons reach to it from the positive terminal through the electrolyte.

 

[alan123hk]

I certainly believe that electrons flow through the battery. I don't know how the complex chemical reaction inside the battery works. But according to the law of conservation of charge, if electrons flowing into the positive electrode do not flow out of the negative electrode, where do those electrons go? If the electrons coming out of the negative electrode did not come from the positive electrode, where did these electrons come from?

Also, I don't think chemical reactions can convert electrons entering the battery into other non-electron particles, and then convert them back into electrons to flow out of the battery.

Please correct me if I'm wrong.

 

[phinds]

I found this https://www.science.org.au/curious/technology-future/batteries#:~:text=A battery is a device,be used to do work. but it also appears to say that electrons flow from one end to the other.

https://van.physics.illinois.edu/qa/listing.php?id=583&t=which-way-do-the-electrons-flow-in-a-battery

 

[nasu]

The chemistry in the electrolite depends on the type of battery. Hovewer, in general electrons travel through the electrolite but not as free, individual electrons. At the positive terminal the electrons attach themseles to some atom producing a negative ion and this is released in solution and travels to the other electrode. Here there is another reaction and the negative ion becomes neutral and the electron is "released" in the metalic electrode an from there it participates in the current in the external circuit. So, electrons move through the electrolite but not as in a metal. They piggy-back on some atom which takes them to the other side of the electrolite sea. Like in a boat. And indeed, they move from plus to minus inside the battery. The convenational current goes from minus to plus inside the battery.

 

[vcsharp2003]

As you said, electrons reach the positive terminal due to the current in the rest of circuit. If these electrons didn't flow -through the electrolyte - to the negative terminal then the charge of the positive terminal would become zero or negative after sometime. Similarly for the negative terminal if it would keep releasing electrons to the rest of circuit, it would become zero charged or positively charged unless of course electrons reach to it from the positive terminal through the electrolyte.

Actually after some more research, I've found that electrons do not flow through the battery, they only flow through the external circuit. If electrons actually flowed through the battery, then that could short the battery or make it too hot.

What actually happens is that to start with the negative terminal already has an excess of electrons due to an oxidation chemical reaction that occurred between the -ve electrode and an electrolyte ion like hydroxyl ion, that results in release of electrons at -ve electrode. But this reaction is stopped when the battery is not connected. So, to start with we have a battery that has potential difference between it's two electrodes since electrons are already deposited on negative electrode, but the chemical reaction in battery is not occurring between the electrodes and electrolyte in unconnected state.

Now, when we connect the battery to an electric circuit, then the electrons on negative electrode get a chance to move towards the +ve electrode but from outside the battery (inside the battery a separator prevents electrons from flowing to +ve electrode else a battery would be useless to end users). These electrons then reach the +ve electrode from the external circuit, where the electrode material, electrolyte and the electron chemically react to produce ions and the electrode undergoes a reduction reaction. The ion produced at +ve electrode (hydroxyl ion) due to the reduction reaction goes into the electrolyte, which then reacts with the -ve electrode material resulting in a chemical reaction causing loss of electrons. These lost electrons in oxidation of -ve electrode get deposited in -ve terminal and continue to flow in external circuit.

The above cycle of reaction at +ve electrode followed by a reaction at -ve electrode continues as long as electrons keep flowing to +ve electrode and it keeps producing electron on the -ve terminal side. So, electrons are not flowing through the battery but a set of chemical reactions are occurring that result in electrons accumulation on -ve terminal.

 

[hutchphd]

Look up Lead -Acid battery. Charging the battery makes the electrolyte more acidic (sulfuric acid)...this means more free protons. They happily gobble electrons making the battery work

EDIT:good you already did!

 

[Delta2]

Now, when we connect the battery to an electric circuit, then the electrons on negative electrode get a chance to move towards the +ve electrode but from outside the battery (inside the battery a separator prevents electrons from flowing to +ve electrode else a battery would be useless to end users). These electrons then reach the +ve electrode from the external circuit, where the electrode material, electrolyte and the electron chemically react to produce ions and the electrode undergoes a reduction reaction. The ion produced at +ve electrode (hydroxyl ion) due to the reduction reaction goes into the electrolyte, which then reacts with the -ve electrode material resulting in a chemical reaction causing loss of electrons. These lost electrons in oxidation of -ve electrode get deposited in -ve terminal and continue to flow in external circuit.

Ok if I understand well from this, electrons don't exactly flow as free electrons through the electrolyte, but they use hydroxyl ions as carriers. So in an attempt to reconcile my former view with this, I would say that inside the battery we have the equivalent of an electron flow from positive to negative terminal.

 

[hutchphd]

It is a little more involved. If someone actually understands chemistry correct me. Check this out

 

[vcsharp2003]

So in an attempt to reconcile my former view with this, I would say that inside the battery we have the equivalent of an electron flow from positive to negative terminal.

Yes, I think so. But the chemical reaction in the battery occurs as long as the electrons flow in external circuit to reach the +ve terminal. If the circuit is switched off then the electron flow stops in external circuit and chemical reaction in the battery stops too.

 

[vcsharp2003]

It is a little more involved. If someone actually understands chemistry correct me. Check this out

This seems to be like a car battery. The hydroxyl ions I referred to in post#17 was for a dry cell battery used in appliances like flashlight etc.

 

[hutchphd]

You have wandered out of my knowledge base. There are many, many, kinds of dry cells. I feel quite certain that many different processes and ions are involved.

 

[jbriggs444]

Through the discharge cycle of a battery, no single electron (or electron-equivalent carried as an ion) will ever make it from the positive terminal, through the battery and back out the negative terminal.

At most, you'll have an electron-equivalent making it partway through one cell. Meanwhile there are other electrons or electron-equivalents drifting through the wire and through the other cells.

 

[hutchphd]

no single electron (or electron-equivalent carried as an ion) will ever make it from the positive terminal, through the battery and back out the negative terminal.

And, of course, how could you know?

 

[jbriggs444]

And, of course, how could you know?

Model and calculate. Just like we "know" most things. Though you are right of course, it's not like we can spray-paint a tag on an electron and track it.

 

[vcsharp2003]

You have wandered out of my knowledge base. There are many, many, kinds of dry cells. I feel quite certain that many different processes and ions are involved.

My source of knowledge was this link

 

[hutchphd]

So that is why these batteries are called generically "alkaline cells" I guess. There are of course many other chemistries. Thanks.

 

[vcsharp2003]

So that is why these batteries are called generically "alkaline cells" I guess. There are of course many other chemistries. Thanks.

The link I mentioned explains very nicely how electrons are released on the -ve electrode via a chemical reaction and then these electrons flow through the conductor in external circuit. But how about the free electrons in the conductor? Are they not supposed to flow to create a current. I was taught that a conductor has free electrons which move under the electric field created within it by the potential difference.

So, I'm trying to understand whether it's the battery electrons or the conductor electrons that contribute to the electric current in the conductor?

UPDATE 1
The battery electrons must also flow in addition to the conductor electrons else the electrons in conducting wire will get exhausted and current flow will stop. So, initially the conductor electrons move but then the battery electrons will always need to flow to maintain a constant flow of electrons.

 

[jbriggs444]

So, I'm trying to understand whether it's the battery electrons or the conductor electrons that contribute to the electric current in the conductor?

It is not clear what you are asking. What do you mean by "contribute to"?

I mean, obviously it is the motion of charges (electrons) in the conductor which defines the electric current in that conductor. But I do not know whether that fits what you mean by "contributes to".

 

[Delta2]

I still remember a phrase from my physics textbook in the secondary high school (ages 15-18, we call it Lykeio here in Greece), (direct translation from Greek follows):
"An EMF source doesn't supply a circuit with electric charge but it sets in motion the electric charge already present in the circuit"

Tbh I am not sure if this phrase is 100% correct but I am just mentioning it...

 

[vcsharp2003]

It is not clear what you are asking. What do you mean by "contribute to"?

I mean, obviously it is the motion of charges (electrons) in the conductor which defines the electric current in that conductor. But I do not know whether that fits what you mean by "contributes to".

By contribute I meant move in the conducting wire of external circuit. Do the battery electrons on its -ve electrode/terminal also move as a current I in the external circuit or its the conductor electrons only that move as a current I ? I got the answer as mentioned in UPDATE 1 of my post. Both i.e conductor electrons as well as battery electrons will move through the conductor wire when current I flows through it

 

[vcsharp2003]

An EMF source doesn't supply a circuit with electric charge but it sets in motion the electric charge already present in the circuit

I see a catch in above statement. Once all free electrons in conductor have flown to the +ve electrode of battery in the external circuit, then there will no more free electrons left in the conducting wire and so the current would stop due to lack of free electrons . Right? So, the battery must supply electrons to maintain the flow i.e to maintain the current.

 

[hutchphd]

There is no way to tell. Electrons are indistinguishable by the tenets of Quantum Mechanics. Somehow batteries use stored energy to internally segregate charge to maintain a fixed electrical potential across their electrodes. That's what they do: the details usually involve selective motions of various charged items: the details are interesting but not directly salient. When an external conductor is attached to the battery electrodes, charges move to mimize this potential energy. Usually the conductor is a metal and the charges that are mobile are the "conduction" electrons. The energy is in fact carried by the associated fields. The rest is detail.

/

 

[jbriggs444]

I see a catch in above statement. Once all free electrons in conductor have flown to the +ve electrode of battery in the external circuit, then there will no more free electrons left in the conducting wire and so the current would stop due to lack of free electrons . Right? So, the battery must supply electrons to maintain the flow i.e to maintain the current.

Have you looked at the electron drift velocity for a wire, divided the wire length by the drift velocity and compared the result to the discharge lifetime of the battery at the current in question?

Wikipedia has a numerical example for drift velocity.