TBR Galvanic Cells increasing voltage

[Meredith92]

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TBR says that "The voltage for a cell is calculated by summing the reduction half cell potential and oxidation half cell potential...To increase the voltage for a galvanic cell, the concentrations of the ions in the cathode solution can be increased or the concentration of the ions in the anode solution can be decreased. the more a reaction can proceed in the forward direction the greater its voltage"

However, half cell potentials DO NOT depend on #of electrons... they are "intensive" properties (as TBR described earlier) so why can changing the concentrations of ions (and thus changing the # of electrons transferred) change the voltage? i understand it would change the free energy (since that DOES rely on the # of electrons), but i dont see how concentration can effect the half cell potentials/ the total cell voltage.


Thanks for your help in advance!

 

[milski]

There are two things making the electrons move: difference in electrical potential and difference in concentration gradient. The potential of the cell is the combination of these two. While the number of electrons moving does not change the potential, how many electrons (and ions) are on one side vs the other does change how easy it is for the electrons to move between the two half-cells.

 

[Meredith92]

Ok that makes sense thank you!

 

[MedGrl@2022]

There are two things making the electrons move: difference in electrical potential and difference in concentration gradient. The potential of the cell is the combination of these two. While the number of electrons moving does not change the potential, how many electrons (and ions) are on one side vs the other does change how easy it is for the electrons to move between the two half-cells.

Is this why E=Eº-(0.06/n)log(Q)... is E not intrinsic but Eº is? Also, is the equation really E=Eº-(0.06/n)log([cathode]/[anode]) based on what Meredith said.

 

[milski]

Is this why E=Eº-(0.06/n)log(Q)... is E not intrinsic but Eº is? Also, is the equation really E=Eº-(0.06/n)log([cathode]/[anode]) based on what Meredith said.

Ε is an intensive property. Being intensive does not mean constant under all conditions, it just means that it does not change when extensive properties like quantity/mass are changed. In other words, a scoop of substance from the beaker will have the same intensive properties as the substance in the beaker.

Ε and Ε0 are both intensive - Ε0 is just E under [arbitrary] standard conditions, like concentration of 1 M.

 

[sshah92]

Just wanted some clarification on this topic please. If you increase the concentration of ions in the anode (say Zn2+ in solution, for example), the electrons from zinc will prefer to jump into solution rather than travel through the wire to the cathode side to reduce the anion (say Cu2+). Is this why voltage decreases when you increase the concentration of ions in the anode solution?

If that's the reason, then wouldn't the very existence of the salt bridge preclude this from happening? In which case the voltage would not be affected by ion concentration?

Thanks for the clarification in advance!

 

[anticarbon]

Doesn't high concentration of cations in anode half-cell resists more metals oxidizing and being released into the solution, therefore decreasing the ability of anode to produce electrons?

I think the presence of salt bridge is to balance the overall charge in both anode and cathod half cells; since anode cell is increasing in positive charge over time, some negatively charged ions, like SO4- or Cl-, travel through the salt bridge to balance out the charge.

For experts out there, please do correct me if I am wrong.