Standard Electrode Potential

Standard Electrode Potential

The hydrogen electrode can now be combined with any suitable half-cell (metal or gas) electrode and the potential difference between the two half-cells determined. If a standard hydrogen electrode is combined with a metal electrode dipping in 1M metal ions at 25°C, the measured potential difference is the standard electrode potential of the metal since by definition E°H/H+ =0 V.
A galvanic cell consisting of the hydrogen electrode and the copper half-cell is written as:
Pt, H2(g) (1 atm)/H+(aq) 1MJ//Cu2+ (1 M)/Cu(S)
The single vertical line represents the separation of phases (e.g. solution and solid) and the double vertical lines represent the salt-bridge.
The standard procedure of writing the electrochemical cell is to place the hydrogen electrode on the left-hand side and the other electrode on the right-hand side. The measured potential difference of such a cell under standard conditions is called the standard electrode potential or the standard reduction potential of the electrode under study and is given the symbol E°. If the left electrode is another one other than the hydrogen electrode, then the measured potential difference is the standard potential of the cell.

The measured potential difference (or cell electromotive force, e.m.f) of the above cell under standard conditions is 0.34V. This is the standard e.m.f of the cell and also the standard electrode potential of the copper half-cell (or copper electrode).

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