concentration cells

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Dina Marchenko 2J
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Joined: Thu Jul 25, 2019 12:16 am

concentration cells

Postby Dina Marchenko 2J » Sun Mar 08, 2020 12:34 pm

Why does a difference in concentrations cause a flow of electrons? And why do the electrons flow from low concentration to high concentration? Is there still a redox reaction taking place? Or is it something else?

Rory Simpson 2F
Posts: 106
Joined: Fri Aug 09, 2019 12:17 am

Re: concentration cells

Postby Rory Simpson 2F » Sun Mar 08, 2020 12:53 pm

In concentration cells, the same half reaction is occurring but in opposite directions. For the lower concentration, the half reaction would be increasing the amount of the species in solution, while the half reaction for the higher concentration would decreased the amount. The transfer of electrons results from the potential difference created as the species tries to reach equilibrium.

Naji Sarsam 1F
Posts: 104
Joined: Sat Aug 17, 2019 12:18 am

Re: concentration cells

Postby Naji Sarsam 1F » Sun Mar 08, 2020 1:59 pm

To clarify, the reaction is still considered a redox reaction. However, it is also important to note that the standard cell potential of every concentration cell equals 0.

Naneeta Desar 1K
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Joined: Fri Aug 09, 2019 12:15 am

Re: concentration cells

Postby Naneeta Desar 1K » Sun Mar 08, 2020 3:06 pm

In concentration cells the E°cell is always 0.

Manav Govil 1B
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

Re: concentration cells

Postby Manav Govil 1B » Sun Mar 08, 2020 3:50 pm

You will need to use the Nernst equation for most concentration cell questions, especially for finding Ecell or a concentration of a half-cell. Just like the comment before this one says, E°cell = 0, and we have to apply this information to get more information.

Posts: 105
Joined: Sat Aug 17, 2019 12:16 am

Re: concentration cells

Postby Mulin_Li_2J » Sun Mar 08, 2020 3:51 pm

The concentration causes electron flow because Ecell is concentration-dependent, whose value can be calculated with the Nernst equation, Ecell = E*cell - (RT/nF)lnQ. In a concentration cell, E*cell equals 0 because anode and cathode have the same redox couples, and therefore same E* value under standard conditions. Thus, we can rewrite this equation as Ecell = - (RT/nF)lnQ.

Think of Le Chatlier's principle, to reach chemical equilibrium, the low concentration electrode wants to dissociate more ions. In the process of producing ions, electrons are released and transferred to the other electrode, forming a current. Thus, electrons flow from low concentration to high concentration.

Hope this can help!

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