# Standard Electrode Potential

It is potential difference developed between metal electrode and the ions of the solution of a molar concentration or 1 atm. pressure at 298 K [25°C]. It is denoted by $E^0$.

It is important to know that the absolute value of or $E^0$or E cannot be determined as neither oxidation nor reduction reaction of half-cell occurs alone. Moreover we have to use a reference electrode i.e. an electrode with known value of electrode potential.

The common reference electrode used is standard or normal hydrogen electrode which can work both as a cathode or an anode.

It is represented as follows,

$Pt, H_2(1 atm) | H^+(1 M)$

Calomel electrode is also used as a secondary reference electrode.

Standard electrode potential

The value of S.H.E. $E^0$ is taken as zero. Cell potential or E.M.F. It is the difference of electrode potential between the two half cells.

Or

It is the potential difference when no current is flowing in the circuit.

• It is measured by potentiometer.

It is also known as cell voltage.

$E^0_{cell} = E^0_{cathode (R.H.S)}- E^0_{anode (L.H.S)}$

E. g. For denial cell:

$E^0_{cell} = E^0_{cathode (cu)}- E^-_{anode (Zn)} \\[3mm] 0.34- (-0.76) \\[3mm] = 1.1 volt.$

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