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Positive vs Negative E value

Posted: Mon Feb 18, 2019 7:37 pm
by ChathuriGunasekera1D
Hi! I had a quick question about determining how you know if the Ecell is positive or negative. I know that it's positive if the cathode is right and negative if the cathode is on the left, but the electron flow always goes towards the cathode regardless of what side the cathode is on. I'm wondering what difference a positive or negative sign makes on the value of Ecell. Thank you!

Re: Positive vs Negative E value

Posted: Mon Feb 18, 2019 8:13 pm
by Toru Fiberesima 1L
The Ecell value is obtained from the two half reactions or the balanced chemical equation. Ecell is E(cathode) minus E(anode). For deltaG to be negative, which indicates that the reaction is a spontaneous one, E cell must be positive.

Re: Positive vs Negative E value

Posted: Wed Feb 20, 2019 12:37 am
by Angel Chen 2k
You determine the Ecell value from the two half-reactions you write from either the cell diagram given or the balanced chemical equation. The formula for calculating the Ecell is E(cathode) - E(anode) ( these values can be obtained from the book standard E value chart ). For example, electrolytic cells, which occur only with the input of an external energy source, E cell is negative because they are nonspontaneous.

Re: Positive vs Negative E value

Posted: Wed Feb 20, 2019 2:16 pm
by Philipp_V_Dis1K
The E value does not depend on the right or left, it is on the E potential of the cathode and anode.

Re: Positive vs Negative E value

Posted: Wed Feb 20, 2019 2:40 pm
by daniella_knight1I
The e value will depend on the overall value of the cell which you get by adding the two half-reactions together to get the overall value.

Re: Positive vs Negative E value

Posted: Wed Feb 20, 2019 3:15 pm
by Katelyn Pham 4E
Ecell = Cathode(right)-Anode(left) and this is found from the half oxidation and reduction equations.