-3

Why is it that metal atoms , experience this potential difference when immersed only in their salt solutions. When they are in contact in real life we cannot see current conducting through it.

Naveen V
  • 105
  • 3

1 Answers1

1

It is not that metal atoms get potential difference. Rather electrons experience different potentials.

Reactions $\ce{M(s) <=> n e- + M^{n+}(aq)}$ effectively serve as charge pumps, aiming for different metal potentials $E = E^{\circ}_{\ce{M/M^{n+}}} + \frac{RT}{nF}\ln{a(\ce{M^{n+}(aq)})}$

The potentials are in context of electrochemistry referring to the standard hydrogen electrode.

Kinetic reasons may cause troubles to reach the equilibrium potentials, sometimes even for open circuits.

At boundary of a metal and a solution of its salts, there are ongoing two chemical reaction in the opposite direction:

  • Metal dissolution $\ce{M(s) -> n e- + M^{n+}(aq)}$:
    • It is decreasing the metal potential by decreasing the metal net charge.
    • The reaction rate is exponentially decreasing with the potential decreasing, establishing the negative loopback and slowing down.
  • Metal deposion $\ce{M^{n+}(aq) + n e- -> M(s)}$:
    • It is increasing the metal potential by increasing the metal net charge.
    • The reaction rate is exponentially decreasing with the potential increasing, establishing the negative loopback and slowing down.

As the result, the metal reaches such a potential both reactions have the same reaction rate and the net reaction rate is zero.

If the circuit is closed, the metal potentials are disturbed and there is ongoing the net reaction to reestablish the equilibrium potential.

Poutnik
  • 41,273
  • 3
  • 49
  • 106
  • So it is the electrons of the metal , that experience different potentials to possibly reduce the metal atom or oxidize the metal atom , and this value is intrinsic to the metal and when measured with reference to hydrogen electrode we tell its the Standard Electrode potential ? – Naveen V Oct 06 '23 at 08:20
  • 2
    It seems to me you may be very confused and may need to set some very basic foundations of electrochemistry, as each answer may easily lead to 2-3 questions. Q/A sites are not best suited for that. Consider reviewing the rich study material at libretexts.org, like Google search results for site:libretexts.org electrochemistry metal electrode potential // I will update my amswer, but consider online review, using this Q/A site rather just for filling the gaps. – Poutnik Oct 06 '23 at 08:36
  • 1
    @NaveenV - Remember this is for aqueous solutions. // Bare electrons aren't stable in aqueous solution so a single half cell reaction can't be measured. Hence the Standard hydrogen electrode as the reference point. // Some metals have more than one oxidation state. // The equation for E that Poutnik gives is the Nernst equation and is for an infinitesimal current flow. For a real battery the voltage drops as the current increases. – MaxW Oct 06 '23 at 08:39
  • Thank you very much , for the answer as well as linking me to further material that is very kind of you , in my country the books just give the information and I find it hard to intuitively learn , but I will refer to the resources @Poutnik – Naveen V Oct 07 '23 at 10:56
  • @MaxW , is that due to the EMF of cell being a constant so , As $I$ increases the internal resistance contributes to the decrease in external potential difference – Naveen V Oct 07 '23 at 10:57
  • 1
    EMF of cells is not constant, it depends on multiple factors. It changes with local changes of cell chemical composition. Its decrease under load is complex function of many factors, like internal resistance, rate of diffusions, geometry, rate of chemical reactions at electrode/electrolyte interface. – Poutnik Oct 07 '23 at 11:02
  • oh okay thank you @Poutnik , one small clarification why is it that only when the circuit is closed metal potentials are distributed , is it because when these two metals are in contact , they feel a potential difference such that a reaction in anode (and cathode) dominates over the other ? – Naveen V Oct 07 '23 at 11:12
  • What do you mean by "metal potentials are distributed"? // Out of the cells, on the level of cell contacts and circuitry between them, the cell is nothing else but a power source, admitting with complicated electronic characteristics. – Poutnik Oct 07 '23 at 11:19