How do molecules in a voltaic cell interact?

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If we put zinc rod in CuSO₄ solution it seems very obvious that they zinc and Cu²⁺ can interact and electrons can be pulled and pushed and one can grab electron and one can loose but in case of voltaic cell it seems magical that they are interacting and I tried to find its answer and I unable to find it.
Thanks.
 

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  • #2
Borek
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What is different in the voltaic cell?
 
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What is different in the voltaic cell?
In direct contact they are interacting at atomic scale but if we see in voltaic cell they are interacting on macroscopic scale and we know electric forces decreases drastically with increase in distance so I think there should be almost no interactions in voltaic cell.
 
  • #4
Borek
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Macroscopic scale is a sum of zillions of microscopic scale events. Reactions take place on the surface, not remotely.
 
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epenguin
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If we put zinc rod in CuSO₄ solution it seems very obvious that they zinc and Cu²⁺ can interact and electrons can be pulled and pushed and one can grab electron and one can loose but in case of voltaic cell it seems magical that they are interacting and I tried to find its answer and I unable to find it.
Thanks.
Where you say pulled and pushed, grabbed and lost, in more highfalutin language a system is out of equilibrium and in one case gets nearer to equilibrium transferring electrons from a Zn atom to a Cu2+ ion. The difference in the case of the voltaic cell is that the electrons lost by the Zn are given to the Cu2+ in a different place and this is rendered possible by the miracle of metallic conductivity.So that's the miracle if there is one. But you've probably accepted that and not considered it a miracle.We all do whether or not we know the theory of it, which is quantum mechanical and not elementary it turns out.

Better read some other explanations this to help get used to it - I often find Chenistry Libre quite clear. https://chem.libretexts.org/Bookshe...cal_Chemistry)/Electrochemistry/Voltaic_Cells

As for it being a miracle, I don't think you're that wrong – maybe we mustn't let anyone hear us calling anything a miracle as we do get to an explanation, but it is still a marvel, and part of a set of what were the most marvellous discoveries about the nature of matter ever - I've never got over it!
 
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Better read some other explanations this to help get used to it - I often find Chemistry Libre quite clear. https://chem.libretexts.org/Bookshe...cal_Chemistry)/Electrochemistry/Voltaic_Cells
I read all this text and they talked nothing about my question and yes I too find text by chemistry libre helpful but not this time😩.

Is tried to answer this question with the help of borek's 4th post and I thought due to large no. Of Cu²⁺ ions there will be some pull on zinc electrode due to which zinc atoms will be oxidised.
Please tell me of I am wrong.
 
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Drakkith
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Is tried to answer this question with the help of borek's 4th post and I thought due to large no. Of Cu²⁺ ions there will be some pull on zinc electrode due to which zinc atoms will be oxidised.
Please tell me of I am wrong.
I don't think that's right. Think of it this way. If the zinc only reacts because of the Cu ions, wouldn't the copper electrode only react because of the pull of the zinc ions? Which one comes first?

As far as I understand it, the reaction at the zinc anode is not the result of a pull by the copper ions at the cathode. It is instead a natural reaction between the zinc in the anode and the solution it is immersed in. The other half-cell exists to accept electrons and supply negative ions to the first cell to keep a voltage from building up between the electrode and the electrolytic solution, which would stop the reactions. Ideally the composition of this 2nd half-cell is chosen so that the electrode spontaneously reacts with solution in a reduction reaction, which adds an additional source of energy to the entire cell.

In other words, both half-cells react spontaneously with their solutions, and are connected together in order to prevent the buildup of a voltage in each half-cell.

Note that the electrolyte is full of mobile charge carriers in the form of positive and negative ions. These will easily move with the application of even a small voltage, just like the electrons in a conductor. The two electrodes can interact with each other because they are connected by the electrolyte and the external circuit. So an oxidation reaction at the anode creates a small charge imbalance, which then propagates through the electrolyte and the external circuit as charge carriers move under this voltage. Then at the cathode a reduction reaction occurs which neutralizes this charge imbalance (or vice-versa, the order is unimportant). Under normal operation you will have huge numbers of these reactions occurring simultaneously, with an accompanying electric current in both the external circuit (e-) and the electrolyte (ions).

Someone correct me if I'm wrong.
 
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  • #8
epenguin
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I read all this text and they talked nothing about my question and yes I too find text by chemistry libre helpful but not this time😩.

Is tried to answer this question with the help of borek's 4th post and I thought due to large no. Of Cu²⁺ ions there will be some pull on zinc electrode due to which zinc atoms will be oxidised.
Please tell me of I am wrong.
The Chem Libre talks about a different metal, but staying with Zn and Cu there are the Wikipedia articles https://en.wikipedia.org/wiki/Galvanic_cell https://en.wikipedia.org/wiki/Daniell_cell
I don't see what is so difficult about the concept of an electron being withdrawn from one metal and donated to another in a different place allowed by conduction instead of an adjacent place. Instead I'd even think in a different place is easier to imagine what actually happens, as locally you are dealing with a more homogeneous situation.

You seem to be asking about physically what in particular is driving it. That's a secondary question compared to the main factor to grasp – that the identical same factors are driving the straightforward chemical reaction as drive the one with the electric current. Whatever these factors are.

Crudely the setup Zn(s) + Cu2+(aq) has more energy than Zn2+(aq) + Cu(s), which will make the spontaneous tendency for the first pair to be transformed into the second, transferring electrons, one way or another. So the energy of four components come into it.The first pair is different from the other pair so there has to be an energy difference; which way round is another matter.

It turns out, the articles tell us, there is not much difference in the energies of the hydrated cations, so this is not an important factor.That however is not a fact you could be expected to know. More important, we are told, is how the metal atoms fit in the solid metal structures. The Zn atoms fit less comfortably into their solid structure than the Cu atoms into theirs. The reason for this we are told is that the electrons in transition metal solids can form what they call d-orbital bonding, which seems something like the metal-ligand bonds that transition elements also form. To which, depending what level you have reached in chemistry, you might be saying "if you say so". Sort of thing that transition elements do. But nothing the inventors of the original cells could have predicted. I don't know that even the direction of the reaction is predictable, maybe someone at home more than me with these things could point out some systematic tendencies from which it is.

Maybe instead of messy chemistry some clean physics would illuminate you? :oldbiggrin:
An electrochemical cell does not need two different metals – both of the electrodes could be Zn. Then if they are in solutions of different Zn2+ concentrations there will be a calculable electrical potential that depends only on the concentration ratio.All the complicating or incalculable factors will cancel as they are the same for both sides.The direction of electrons flow will be that which tends to make more equal the two concentrations (from the more dilute to the more concentrated solution).
 
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The Chem Libre talks about a different metal, but staying with Zn and Cu there are the Wikipedia articles https://en.wikipedia.org/wiki/Galvanic_cell https://en.wikipedia.org/wiki/Daniell_cell
I don't see what is so difficult about the concept of an electron being withdrawn from one metal and donated to another in a different place allowed by conduction instead of an adjacent place. Instead I'd even think in a different place is easier to imagine what actually happens, as locally you are dealing with a more homogeneous situation.

You seem to be asking about physically what in particular is driving it. That's a secondary question compared to the main factor to grasp – that the identical same factors are driving the straightforward chemical reaction as drive the one with the electric current. Whatever these factors are.

Crudely the setup Zn(s) + Cu2+(aq) has more energy than Zn2+(aq) + Cu(s), which will make the spontaneous tendency for the first pair to be transformed into the second, transferring electrons, one way or another. So the energy of four components come into it.The first pair is different from the other pair so there has to be an energy difference; which way round is another matter.

It turns out, the articles tell us, there is not much difference in the energies of the hydrated cations, so this is not an important factor.That however is not a fact you could be expected to know. More important, we are told, is how the metal atoms fit in the solid metal structures. The Zn atoms fit less comfortably into their solid structure than the Cu atoms into theirs. The reason for this we are told is that the electrons in transition metal solids can form what they call d-orbital bonding, which seems something like the metal-ligand bonds that transition elements also form. To which, depending what level you have reached in chemistry, you might be saying "if you say so". Sort of thing that transition elements do. But nothing the inventors of the original cells could have predicted. I don't know that even the direction of the reaction is predictable, maybe someone at home more than me with these things could point out some systematic tendencies from which it is.

Maybe instead of messy chemistry some clean physics would illuminate you? :oldbiggrin:
An electrochemical cell does not need two different metals – both of the electrodes could be Zn. Then if they are in solutions of different Zn2+ concentrations there will be a calculable electrical potential that depends only on the concentration ratio.All the complicating or incalculable factors will cancel as they are the same for both sides.The direction of electrons flow will be that which tends to make more equal the two concentrations (from the more dilute to the more concentrated solution).
It is not clicking why does this happens😩.
I think I should do a tonnes of questions and after that when I would be easy with this I will try again to see this post.
Thanks for helping me😇.
 

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