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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!
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.
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.
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