# How Do You Calculate Expected Cell Voltage in Electrochemistry?

• leaf345
In summary, the speaker performed a lab on electrochem and was asked to calculate the expected cell voltage. They used the Nernst equation and considered the concentrations of Ag+ and Cu2+ in their solution. They were unsure about the value of n and the correct equation for Q. The speaker also encountered difficulty with another cell they performed, involving Ag+ and Fe2+. They used the Nernst equation again but got a negative value for the expected cell voltage. They questioned if they had performed the calculation correctly.
leaf345
Hey guys, I just did a lab on electrochem but we haven't started learning this in our lectures so I'm not too confident on it. One of the lab question asks us to calculate the expected cell voltage. From reading the textbook, this is what I did:
The reaction was 2Ag+ + Cu -> 2Ag + Cu2+
I added reduction potentials of Ag and Cu to get 0.46V for the standard voltage. Then I used the nersnt eq'n
E= 0.46 -(0.05915/n)*logQ
What I'm not sure about is...
We used 0.1 M AgNO3 and Cu(NO3)2, so would n be 2 or 0.2?
And would Q= [0.1 Cu2+][1]/[0.1 Ag+]^2*[1]=10?
Help would be appreciated!

Also, we did another cell that is giving me trouble too.
One 1/2 cell was:
Ag electrode
0.1 M AgNO3 solution

The other was:
Pt electrode
0.1 M Fe2+ and 0.1 M Fe3+

I think the overall redox rx'n was Ag+ + Fe2+ --> Fe3+ + Ag
so I calculated the expected cell voltage. But I get a value that is opposite to the sign of the voltage we observed.
What I did was
E=Eo -(0.05915/n)*logQ
where Eo= 0.8-0.77 because that is the difference between the redox potentials of Ag and Fe.
n=1 electron
Q= [Fe3+]/[Fe2+]*[Ag+] = 0.1/(0.1*0.1)=10
so E= negative something

Am I doing this one correct?

Hello,

It's great that you're taking the initiative to learn and apply electrochemistry in your lab work. As for your question, n in the Nernst equation represents the number of electrons exchanged in the reaction. In this case, since 2 Ag+ ions are reduced to 2 Ag atoms, n would be 2. Additionally, Q represents the reaction quotient, which is the ratio of the product concentrations to the reactant concentrations. In this case, since the concentrations of both Ag+ and Cu2+ are 0.1 M, Q would be 1. So, your calculations seem to be correct.

However, it's important to note that the Nernst equation is only applicable to cells at equilibrium. If your lab experiment was not performed under equilibrium conditions, then the calculated cell voltage may not accurately represent the expected value. I would recommend discussing this with your instructor to ensure that your calculations are valid.

Overall, it seems like you have a good understanding of the concepts and equations involved in electrochemistry. Keep up the good work and continue to ask questions and seek clarification when needed. Best of luck with your studies!

## 1. What is electrochemistry?

Electrochemistry is a branch of chemistry that deals with the study of chemical reactions that involve the transfer of electrons between substances.

## 2. What are the applications of electrochemistry?

Electrochemistry has many practical applications, including the production of metals, batteries and fuel cells, corrosion prevention, and wastewater treatment.

## 3. What is an electrochemical cell?

An electrochemical cell is a device that converts chemical energy into electrical energy through a redox reaction. It consists of two electrodes (anode and cathode) and an electrolyte solution.

## 4. How does electrochemistry contribute to sustainable energy production?

Electrochemistry plays a crucial role in the production of sustainable energy through the development of technologies such as solar cells, fuel cells, and supercapacitors. It also enables the storage of renewable energy in batteries.

## 5. What is the difference between a galvanic cell and an electrolytic cell?

A galvanic cell generates electrical energy from a spontaneous redox reaction, while an electrolytic cell uses electrical energy to drive a non-spontaneous redox reaction. In other words, a galvanic cell is a source of energy, while an electrolytic cell is a consumer of energy.

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