# Unit 5 Section 2 Electrode Potentials

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## Electrochemical Cells - Explanation

Electrode potential: the voltage measured when a half-cell is connected to a standard hydrogen electrode

E.C. Cells can be made from two different metals dipped in salt solutions of their own ions and connected by a wire (the external circuit).(diagram 1)

There are always 2 reactions within an electrochemical cell - an oxidation and a reduction - it's a redox process.

Electrons flow through the wire from the most reactive element to the least reactive.

A voltmeter in the external circuit shows the voltage between the two half-cells. This is the cell potential or e.m.f., E.cell

You can also have half-cells involving solutions of two aqueous ions of the same element, using the standard hydrogen electrode (diagram 2).

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## Calculating Cell Potential

Standard electrode potential = electrode potential on the right-hand side of the equation - electrode potential on the left hand-side of the equation

Cell potential will always be a positive voltage, because the more negative value is subtracted from the more positive value.

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