I How is Potential Difference Created in Electrolytes?

[Dario56]

When we have a resistor in electronic conductors, potential difference is created via surface charges which accumulate on conductor surface.

What about electrolytes?

I am not sure if electrolytes can create potential difference in the same way since surface in electrolytic conductors isn't as well defined as in solid conductors or wires and may not follow the current path in electrolyte.

 

[Dale]

It still functions the same way. Surface charge density still plays the same role as before.

Of course, the surface may move as you say, so you can have “convection currents” caused by bulk movement of the fluid. Usually the motion is slow enough to treat it quasi-statically, but Maxwell’s equations hold regardless.

 

[Dario56]

It still functions the same way. Surface charge density still plays the same role as before.

Of course, the surface may move as you say, so you can have “convection currents” caused by bulk movement of the fluid. Usually the motion is slow enough to treat it quasi-statically, but Maxwell’s equations hold regardless.

So charges accumulate on the surface of the solution or melt of some electrolyte when current flows? If there is a bigger volume of solution, these charges may be far away from when current is flowing so very big charge density may be needed for potential to be big enough where current flows.

 

[hutchphd]

This is complicated. I invite you to look at the plots of internal resistance vs Temperature before settling on any particular generic "cause". Many are surface related . There are competing factors of ion mobility, reactivity, and surface conformation to mention a few. Personally, I rather dislike concept of "electric field between the plates" as being more fraught than explicative.
I suggest examining a particular chemical system (maybe lead- sulfuric acid) in great detail.

 

[Dale]

So charges accumulate on the surface of the solution or melt of some electrolyte when current flows? If there is a bigger volume of solution, these charges may be far away from when current is flowing so very big charge density may be needed for potential to be big enough where current flows.

Sorry, I don’t understand what you are asking here.

 

[Dario56]

Sorry, I don’t understand what you are asking here.

Never mind, but you say it is the same mechanism.

 

[Dale]

Never mind, but you say it is the same mechanism.

Yes. Conductors obey Ohm’s law and EM fields obey Maxwell’s equations the same regardless of the state of matter.

 

[Dario56]

Yes. Conductors obey Ohm’s law and EM fields obey Maxwell’s equations the same regardless of the state of matter.

Well as far as I know not all conductors in all conditions follow Ohm's law. Elctrolytes in batteries do.
I don"t know in what cases Maxwell equations don't hold if we are in field of classical physics?

 

[Dale]

Well as far as I know not all conductors in all conditions follow Ohm's law.

Sure, but those conditions can also be considered the conditions where they stop being conductors. I.e. you can take following Ohm’s law as the definition of a conductor.

The point is that there are fluids which under some conditions follow Ohm’s law and the fact that they are fluid does not prevent them from following Ohm’s law under those conditions.

 

[hutchphd]

The other piece of this is that for linear systems, Thevenin's theorem tells us we can simplify the battery into an ideal voltage source and a resistor.
So it really doesn't matter that it is not that simple and lots of complicated things are going on internally in the battery. We choose this representation because it works well and has some more or less tenuous relation to the internal physics. Worrying about "where is the resistor?" is not a useful enterprise, unless you are designing batteries. Then the answer is not trivial and you can spend a career on it.

 

[tech99]

We do an experiment where we pass a current across a salt soution in a Petri dish using horizontal carbon electrodes. We put a few drops of Universal Indicator in the solution, so the formation of acid, alkali and Chlorine can be seen. This gives a swirling pattern showing the flow of currents and the formation of the products, especially on the surface. I have not studied the form of what is seen in detail but it might be interesting to try.