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Cell Diagram and Ecell

Posted: Tue Feb 26, 2019 9:20 am
by Tarika Gujral 1K
1) With gaseous and nonconducting solid compounds, is the order
Inert|Gas/solid|Chg || Chg|Gas/solid|Inert?
Or does it follow the order of reactants to products?
Inert|Ox Reactant|Ox Product || Red Reactant|Red Product|Inert

2) With a positive Ecell, reduction is always on the right. Is this order reversed when Ecell < 0?

Re: Cell Diagram and Ecell

Posted: Tue Feb 26, 2019 10:35 am
by Jesse Kuehn 1B
I believe the solid is always on the outside (or just inside the inert part) so the second form should always be right, and yes everything is reversed when the E is less than zero.

Re: Cell Diagram and Ecell  [ENDORSED]

Posted: Tue Feb 26, 2019 12:11 pm
by Chem_Mod
Using what I discussed in class, and the example I did in class:

ANODE (LEFT) || CATHODE (RIGHT)

Cu(s) | Cu2+(aq) || Fe3+(aq), Fe2+(aq) | Pt(s)

Put the conducting solids (electrodes) on the outside and aqueous next to the salt bridge.

Always include phase in the equation and cell diagram.

In a homework problem, there is a cell diagram answer key written as: Pt(s) | I- (aq) | I2(s) || .......

This is a saturated I-(aq) solution with undissolved I2(s) in the same solution. Both the salt bridge and the platinum electrode are in contact with the same saturated I-(aq) solution.
As one can see this simple notation does give the information needed to build or visualize the cell (battery).

Another homework problem used KOH (aq) instead of OH- (aq), but you do not need to include K if there is no information about potassium in the question. You can just put OH-(aq) to indicate alkaline conditions.

In cell diagrams: Anode (oxidation half-reaction) is always on the left; and the cathode (reduction half-reaction) is always on the right.

Some homework problems intentionally ask what is wrong with a given cell diagram, and an incorrect notation is given (which one can figure out because the voltage is negative).
By switching the left and right half-reactions one gets the correct cell diagram with a positive voltage.
To be correct the cell (battery) must have a positive voltage (as I repeated and joked about in class :-).

Re: Cell Diagram and Ecell

Posted: Mon Mar 11, 2019 3:20 pm
by jane_ni_2d
how can you tell which is the anode and which is the cathode?

Re: Cell Diagram and Ecell

Posted: Thu Mar 14, 2019 11:01 pm
by davidryan3f
jane_ni_2d wrote:how can you tell which is the anode and which is the cathode?

the anode is always on the right of the cell diagram and the cathode is on the right.

Re: Cell Diagram and Ecell

Posted: Fri Mar 15, 2019 10:43 pm
by riddhiduggal
In which cases do you flip the sign for the E, when calculating Ecell?

Re: Cell Diagram and Ecell

Posted: Sun Mar 17, 2019 2:58 pm
by lukezhang2C
For a Galvanic Cell it should be Anode || Cathode, where there are single lines (|) separating different states of matter, and commas separating different agents with the same state of matter. i.e (aq), (aq), || (aq)| (s)

Re: Cell Diagram and Ecell

Posted: Sun Oct 27, 2019 10:08 pm
by AnayaArnold_3L
Thanks for clarifying!!

lukezhang2C wrote:For a Galvanic Cell it should be Anode || Cathode, where there are single lines (|) separating different states of matter, and commas separating different agents with the same state of matter. i.e (aq), (aq), || (aq)| (s)