[Nitin_Naudiyal]

I was reading about Leclanche's Cell,

It is mentioned that " The Complexation of Zn²⁺ by NH₃ molecules decreases the concentration of Free Zn²⁺ ions. This Increases the Voltage of the cell. "

I want to know, how decrease in the concentration of Zn²⁺ ions increases the voltage of the cell.

Thank you in Advance

[Borek]

Can you write Nernst equation for the cell?

[Nitin_Naudiyal]

Oxidation at Anode:
Zn  Zn²⁺ + 2e^-

Reduction at Cathode:
2NH₄⁺ + 2MnO₂ + 2e^- Mn₂O₃ + 2NH₃ + H₂O

Net Cell Reaction:
Zn + 2NH₄⁺ + 2MnO₂  Zn²⁺ + Mn₂O₃ + 2NH₃ + H₂O

Nernst Equation:

E_cell = E⁰ - 0.0592/2 Log([Zn²⁺][NH₃]²[H₂O]/[NH₄⁺]²)

[Borek]

E_cell = E⁰ - 0.0592/2 Log([Zn²⁺][NH₃]²[H₂O]/[NH₄⁺]²)

Assuming everything else doesn't change and rearranging:

[tex]E' = -\frac{0.0592}{2} \log([Zn^{2+}]) = \frac{0.0592}{2} pZn[/tex]

[Nitin_Naudiyal]

So, as the Concentration of Zn ions decreases, the value of the non standard state electrochemical condition in the Nernst Equation decreases and hence the value of E_cell increases i.e. Potential of the cell increases.

Am i correct ?

[Borek]

Yes, we are dealing with a formal potential.

[Nitin_Naudiyal]

Thank You for your Help