Cell Potentials

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Cell Potentials
× The standard electrode potential of a halfcell, E , is the e.m.f. of a halfcell compared with a
standard hydrogen halfcell, measured at 298K with solution concentrations of 1 mol dm and a gas
pressure of 1 kPa (1 atmosphere).
× The standard cell potential of a cell is the e.m.f. between the two half cells making up the cell
under standard conditions.
× The cell reaction is the overall chemical reaction taking place in the cell.
Standard electrode potentials
× A standard hydrogen halfcell is used as the reference standard for the measurement of cell e.m.f.
× An electromotive force e.m.f is the voltage produced by a cell when no current flows.
We can compare the tendency of different half cells to release or accept electrons by measuring the e.m.f.
when the halfcells are combined separately with a hydrogen halfcell. To make this comparison more
meaningful we use halfcells and standard conditions.
× The resulting e.m.f. is called the standard electrode potential of a halfcell.
× The standard electrode potential of a hydrogen halfcell is defined as exactly 0V.
Measuring standard electrodes
A standard electrode potential is measured by connecting a standard halfcell to a standard hydrogen
halfcell. The reading on the voltmeter gives the standard electrode potential of the zinc halfcell.
Standard cell potentials and cell reactions
× The standard cell potential of any cell is the difference between the standard electrode potentials of
each halfcell.
× The cell reaction is the sum of the reduction and oxidation half reactions taking place in each half

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