A hard electrochemistry question (in my opinion)

In summary: The number that comes to mind is about 96,500 somethings ( coulombs per mole ?)I know this. One faraday constant is equal to one mole of electrons - this is equal to 6.023 \times 10^{23} \times 1.6\times 10^{-19} = 96368 \frac {Coulomb}{mol}Dear Borek, you said one Ampere is one coulomb per second. Then 1,000 amperes are equal to 1,000 coulombs per second. This in turn gives 6.25*1021 electrons per second, which means about 0.01 moles of electrons per second. In the red
  • #1
chem_tr
Science Advisor
Gold Member
609
3
Hello all,

As I am preparing for my PhD proficiency exam, I tried to solve some Analytical chemistry problems. and stuck in one.

The scheme for rechargeable battery, used in automobiles working with electricity, is given below:

Zn(s)|ZnCl2 (aq) || Cl-(aq)|Cl2|C(s)

If the battery gives a current of 1.00*103 amperes, how many kilograms of Cl2 are consumed?

Well, I have attempted to solve this, but have not found enough evidence to study on and solve the problem. What I've done is basicly the following:

The redox reaction might be like this:
[tex]Zn_{(s)}+Cl_2_{(aq)} \longrightarrow ZnCl_2_{(aq)}[/tex]
Nernst formula may reveal something, but the final voltage as well as standard voltage (the latter can be calculated via referring to known tables, though), and we don't know anything about the concentrations. How can I use the current given? If you need, these are the half cell reactions:

[tex]Zn^{2+}+2e^- \rightleftharpoons Zn_{(s)}; E°=-0.764~Volts[/tex]
[tex]Cl_2_{(aq)} + 2e^- \rightleftharpoons 2Cl^-; E°=1,395~Volts[/tex]

I am in need of recommendations, thank you.
 
Chemistry news on Phys.org
  • #2
Actually its quite simple...unfortunately I don't remember exactly how to do it off the top of my head. I'll get back to it later, I'm a bit busy at the moment. The method is usually introduced at the end of the electrochemistry chapter in general chemistry texts.
 
  • #3
Look for Faraday constant.

Or - 1A is a Coulomb/sec, you know the current, you know the charge per second. Every two electrons give one Cl2 particle. You know the charge, you know number of the Cl2 particles consumed per second. Just convert Coulombs to Avogadro number.

That's almost the same - Faraday constant is number of Coulombs in 1 mole of electrons :)


Chemical calculators for labs and education
BATE - pH calculations, titration curves, hydrolisis
 
Last edited:
  • #4
Borek said:
Look for Faraday constant.

The number that comes to mind is about 96,500 somethings ( coulombs per mole ?)
 
  • #5
I know this. One faraday constant is equal to one mole of electrons - this is equal to [tex]6.023 \times 10^{23} \times 1.6\times 10^{-19} = 96368 \frac {Coulomb}{mol}[/tex]
 
  • #6
Dear Borek, you said one Ampere is one coulomb per second. Then 1,000 amperes are equal to 1,000 coulombs per second. This in turn gives 6.25*1021 electrons per second, which means about 0.01 moles of electrons per second. In the redox, two electrons are used as you stated; so 0.005 moles of chlorine are consumed. This means 7.368*10-4 kilograms of chlorine gas are used.

Am I correct, pals? Thank you very much for your help, you all.
 
  • #7
1 mole Cl2 == 2 moles of e- = 2*6.023*10^23*1.6*10^(-19) C = 1.927*10^5 C

1 mole Cl2 == 71 g

So 71 g Cl2 == 1.927*10^5 C

Hence 10^3 C/s == 71/192.7 = 0.368 g of Cl2 consumed per second.

I think you made a typo in the very last step (everything up to that point looks good).

Note that one can only calculate the consumption RATE, since the time of use is not given.
 
  • #8
Thank you, I haven't remembered that one Ampere is equal to one Coulomb per second, so I was stuck. Again, thank you for your help.
 
  • #9

1. What is electrochemistry?

Electrochemistry is a branch of chemistry that studies the relationship between electricity and chemical reactions. It involves the use of electrical energy to cause chemical reactions or the production of electricity as a result of a chemical reaction.

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

A galvanic cell, also known as a voltaic cell, is a device that converts chemical energy to electrical energy. It consists of two half-cells connected by a conductive material and a salt bridge. An electrolytic cell, on the other hand, is a device that uses electricity to cause a chemical reaction. It consists of two electrodes immersed in an electrolyte solution.

3. How do you determine the standard electrode potential of a half-cell?

The standard electrode potential of a half-cell can be determined by measuring the voltage generated by the half-cell in a galvanic cell compared to a standard hydrogen electrode (SHE). The standard electrode potential is defined as the potential of a half-cell under standard conditions (1M concentration, 1atm pressure, and 298K temperature) relative to the SHE, which has a standard electrode potential of 0V.

4. What is the Nernst equation and how is it used in electrochemistry?

The Nernst equation is an equation that relates the standard electrode potential of a half-cell to the concentrations of the reactants and products in a cell. It is often used to calculate the cell potential under non-standard conditions. The equation is E = E° - (RT/nF)ln(Q), where E is the cell potential, E° is the standard electrode potential, R is the gas constant, T is the temperature in Kelvin, n is the number of electrons transferred in the reaction, F is Faraday's constant, and Q is the reaction quotient.

5. Can you explain the difference between a reduction potential and an oxidation potential?

A reduction potential is a measure of the tendency of a species to gain electrons and undergo reduction. It is measured relative to the standard hydrogen electrode (SHE). A more positive reduction potential indicates a greater tendency for reduction to occur. An oxidation potential, on the other hand, is a measure of the tendency of a species to lose electrons and undergo oxidation. It is measured relative to the SHE, with a more negative oxidation potential indicating a greater tendency for oxidation to occur.

Similar threads

Replies
15
Views
3K
  • Chemistry
Replies
5
Views
2K
  • Biology and Chemistry Homework Help
Replies
6
Views
2K
  • Biology and Chemistry Homework Help
Replies
6
Views
2K
  • Biology and Chemistry Homework Help
Replies
1
Views
1K
Back
Top