Redox reactions and electrode potentials
- Redox reactions invovle electron transfer. They can be split into two half equations, one producing electrons and one accepting them.
- Electrochemical cells: consists of two half cells connected by a salt bridge. We measure the maximum potential difference between the two electrodes of the half cells with a high resistance voltmeter, so that negligible current flows.
- The standard electrode potential of a half cell is defined as the potential difference between it and a standard hydrogen half cell.
- Mesurements for the standard electrode potential of a half cell are made at 298K, with the metal dipping into a 1.00moldm-3 solution of a salt of the metal.
- When two half cells are connected to form an electrochemical cell, the half-cell with the more positive standard electrode potential becomes the positive terminal of the cell.
- The half cell with the more negative standard electrode potential becomes the negative terminal of the cell.
- Electrons flow in the external circuit from the negative to the positive terminal.
- An oxidation reaction takes place at the negative terminal and the elctrons produced are supplied to the reduction reaction at the positive teminal. Ecell is the difference between the standard electrode potentials of the two half cells.
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