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As I understand it, the voltage in an electrochemical cell is due to the electrons transferred having a decrease in electrical energy as they go from one species to another.

I assume that this change in potential is due to the electrostatic attractions and repulsions of the protons and other electrons of the species reacting with each other. However, I fail to see how the concentration of species would change the potential difference.

For example, I feel like the change in electric potential for an electron moving from $\ce{Zn}$ to $\ce{Cu^2+}$ in the reaction given below should not depend on the amounts of $\ce{Zn^2+}$ and $\ce{Cu^2+}$ present, just on the atomic level.

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

Could someone please explain why the voltage is not constant, from a conceptual standpoint? I considered that it may be that $\ce{Zn^2+}$ attracts electrons as well, but the solution remains electrically neutral due to the salt bridge, so I am not sure if that is the reason.

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  • $\begingroup$ Your conceptual notion on this is simply incorrect. For an extremely thorough discussion of the findamentals, see this paper: K. Schmidt-Rohr, "How Batteries Store and Release Energy: Explaining Basic Electrochemistry", J. Chem. Ed., 95 (10) (2018) 1801-1810. The Zn and Cu Daniell cell, which is what you specifically ask about, is addressed in great detail. TL; DR Cohesive energy differences are the major factor in explaining the behavior. $\endgroup$
    – Ed V
    Apr 16, 2021 at 11:55
  • $\begingroup$ Thank you, this was exactly what I was looking for. $\endgroup$
    – Akash
    Apr 16, 2021 at 18:00

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