increasing EMF in galvanic cell

[MedGrl@2022]

975. Which of the following will ALWAYS increase the emf of a galvanic cell?

A. Increasing the concentration of the oxidant at the anode.
B. Increasing the concentration of the oxidant at the cathode.
C. Decreasing the internal resistance of the cell.
D. Raising the temperature of the cell.

I guessed A because oxidation occurs at the anode and an oxidant could/should increase the amount of oxidation. I also can see how increasing the concentration of oxidant in the cathode would increase reduction there too because the oxidant would be reduced.

For this equation, I would have used E=Eº-(0.06/2)log(less concentrated/more concentrated). Does it matter which side is more concentrated?

This is EK's answer: "B is correct. The oxidant is at the cathode in the galvanic cell, so A is wrong. Changing the internal resistance won't change the emf, so C is wrong. Raising the temperature won't necessarily increase the emf, so D is wrong. B is correct based on LeChatelier's principle."

Couldn't the oxidant be at the cathode as well as the anode?

Thank you once again for your help! 🙂

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[Postictal Raiden]

975. Which of the following will ALWAYS increase the emf of a galvanic cell?

A. Increasing the concentration of the oxidant at the anode.
B. Increasing the concentration of the oxidant at the cathode.
C. Decreasing the internal resistance of the cell.
D. Raising the temperature of the cell.

I guessed A because oxidation occurs at the anode and an oxidant could/should increase the amount of oxidation. I also can see how increasing the concentration of oxidant in the cathode would increase reduction there too because the oxidant would be reduced.

For this equation, I would have used E=Eº-(0.06/2)log(less concentrated/more concentrated). Does it matter which side is more concentrated?

This is EK's answer: "B is correct. The oxidant is at the cathode in the galvanic cell, so A is wrong. Changing the internal resistance won't change the emf, so C is wrong. Raising the temperature won't necessarily increase the emf, so D is wrong. B is correct based on LeChatelier's principle."

Couldn't the oxidant be at the cathode as well as the anode?

Thank you once again for your help! 🙂

Oxidants get reduced. Reduction takes place at the cathode.

Reductants get oxidized. Oxidation takes place at the anode.

It's a brain twister.

 

[MedGrl@2022]

Oxidants get reduced. Reduction takes place at the cathode.

Reductants get oxidized. Oxidation takes place at the anode.

It's a brain twister.

Couldn't the oxidants oxidize the reductants at the cathode though? Also, I thought voltage was an intrinsic property. However, I guess it is not since the equation E=Eº-(0.06/2)log(more concentrated/less concentrated) exists. So that is a little confusing too. Also which side would I put the anode and cathode in the equation. Do I just need to figure out which one is more and which one is less concentrated? If the less concentrated side starts becoming more concentrated then E could go down though right?

This stuff is a bit confusing. Where is a good resource to learn all of this?

Thank you for your help. Do you think you could help me with my other problem regarding Gº and G, too?

 

[Back 5]

Electrons flow from anode to cathode.

Anode is oxidized (an ox) cathode is reduced (red cat).

Galvanic cells, cathode is positive and anode is negative. I think that's where you got mixed up. Galvanic and electrolytic cells are opposites.

 

[MedGrl@2022]

Oxidants get reduced. Reduction takes place at the cathode.

Reductants get oxidized. Oxidation takes place at the anode.

It's a brain twister.

This probably has to do with if you increase the concentration in the cathode then you increase the emf like in a concentration cell right because..

E=Eº-(0.06/n)(log([anode]/[cathode]))

 

[MedGrl@2022]

Electrons flow from anode to cathode.

Anode is oxidized (an ox) cathode is reduced (red cat).

Galvanic cells, cathode is positive and anode is negative. I think that's where you got mixed up. Galvanic and electrolytic cells are opposites.

Okay I think I get that... so there should never be oxidants in the anode because reductants which become oxidized are needed to release their electrons so that electrons will flow to the cathode and this occurs spontaneously right due to the laws of entropy(?), or is there a chemical that could/would assist the oxidation (or is that very uncommon)?

 

[TieuBachHo]

Okay I think I get that... so there should never be oxidants in the anode because reductants which become oxidized are needed to release their electrons so that electrons will flow to the cathode and this occurs spontaneously right due to the laws of entropy(?), or is there a chemical that could/would assist the oxidation (or is that very uncommon)?

In Galvanic cells, oxidants and reductants are held separated. Oxidants get reduced, so they are cations. Reductants get oxidized, so they are anions. Therefore, oxidants are in the cathode side while reductants are in the anode side. Now, if you increase the concentration of oxidants on the cathode side, you increase the emf.

Electrons come from the solid metal that immerses in the anode side. It loses electrons to the cathode side in spontaneous reaction of a galvanic cell. This happens because of the differences in reduction potentials. Laws of entropy relate to order/disorder of chemical physical states or re-arrangements. Reduction potentials are chemical inert properties. I am not sure how you can equate them.

What do you mean by "a chemical ... assist the oxidation"?

 

[DeFused]

I don't mean to hijack this thread but I am a little confused still on why does increasing concentrations of the ions in the cathode solution increase the voltage?

Maybe I'm thinking a little too simplistic but I know that reduction occurs at the cathode and electrons are flowing from the anode to the cathode and to me that sounds like if you added more ions at the anode, wouldn't you provide more electrons?

Say you have: Zn(s) --> Zn+2 + 2e- occuring at the anode
Cu+2 + 2e- --> Cu(s) occuring at the cathode

To me, it looks Zn is providing the electrons that are flowing from the anode to the cathode. I think I'm missing an important point here because I know from TBR increasing ion concentration at the cathode or decreasing ion concentration at the anode would increase voltage.

EDIT**
The only way this makes sense to me is using the nernst equation where its "-log[anode/cathode]" - therefore if the cathode is larger than the anode it will yield a negative number. The more negative the term is the more positive the potential.

I still don't understand why this happens though