How much electrical energy can be extracted from Iron in a cell?

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Discussion Overview

The discussion revolves around the calculation of electrical energy that can be extracted from an electrochemical cell using iron and iron chloride solutions. Participants explore the reactions occurring at the electrodes, the use of the Nernst equation, and thermodynamic principles to estimate energy output before the cell reaches equilibrium.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant describes a basic electrochemical cell setup with 3 moles of iron and iron chloride, seeking to calculate the energy produced before the cell becomes balanced.
  • Another participant requests the reactions for both electrodes and the Nernst equation, noting that the battery will stop functioning when the potentials are identical.
  • A participant provides the discharge reactions for both electrodes and calculates the overall cell reaction potential, indicating an overall cell voltage of 1.21V.
  • Another participant explains that the Nernst equation can be used to calculate the potential based on ion concentrations and suggests integrating power over the reaction progress to find the energy of the system.
  • This participant also mentions the possibility of calculating energy using thermodynamic principles, specifically Gibbs energy, while expressing uncertainty about their own knowledge on the topic.

Areas of Agreement / Disagreement

Participants express various viewpoints on the calculations and methodologies to determine energy output, with no consensus reached on the best approach or the final energy values.

Contextual Notes

There are limitations regarding the assumptions made about the concentrations of ions and the specifics of the Nernst equation application. The discussion also reflects varying levels of understanding of thermodynamic concepts among participants.

Kisen
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TL;DR
How much electrical energy can be extracted from Iron in a cell?
Hi,
I am trying to get to an answer for the following scenario.

Imagine you have an electrochemical cell in its most basic terms.
On the negative electrode you have 3 moles of iron metal in a chloride solution. On the positive side you have 3 moles FeCl3 solution. These are separated by a membrane. A pretty standard setup.

When you connect a load between the positive and negative electrodes, electrons flow as iron metal oxidises to Fe2 and Fe3 reduces to Fe2.

What i am trying to calculate is how much energy does the above setup produce before the cell becomes balanced?
If not balanced, then what's left over after one of the electrodes reaches a state of all Fe2?

Can anyone help me answer these 2 questions, please.
 
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Can you write reactions for both cells? Can you write Nernst equation for both cells? Battery will stop working when these potentials are identical.
 
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Borek said:
Can you write reactions for both cells? Can you write Nernst equation for both cells? Battery will stop working when these potentials are identical.
Hi,
Here are the reactions during discharge for both side of the cell. I don't know what a Nernst equation is. Will a Nernst equation help me to calculate how much overall energy is in a cell of a given size?

Reactions:

Positive electrode: 2FeCl3 + 2e- -> 2FeCl2 + 2Cl- Eo = 0.77V

Negative electrode: Fe + 2Cl- -> FeCl2 + 2e- Eo = -0.44V

Overall cell reaction: Fe + 2 FeCl3 -> 3FeCl2 Eocell = 1.21V
 
Nernst equation let's you calculate the potential as a function of concentration of ions involved, so it will let you calculate the final potential. It will also let you calculate all intermediate potentials as a function of the reaction progress towards the equilibrium, as concentrations are rather simple function of the reaction stoichiometry - which is in turn easy to combine with the flowing current or charge transfer (through the Faraday's law of electrolysis). VI is power, integrate it from the initial concentration to the equilibrium and you have energy of the system.

It is also definitely possible to calculate the amount of energy from thermodynamics, using Gibbs energy of the system. In theory I should be able to do that, in practice I forgot too much and I prefer to not risk making an idiot out of myself :wink:
 

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