Is the potential for an electrochemical half-cell

(both oxidized and reduced form at c = 1 mol/l) established relative to the potential of 0.000 V for the standard hydrogen electrode

(H⁺/H couple under standard state conditions).

The equilibrium electromotive force E_cell (the potential of the galvanic cell) that is the potential difference between the two

half-cells is measured:

E⁰_cell = E⁰ = E⁰_red – E⁰_ox

Any other reference electrode (which is stable and the potential known) may be used for measurement of electrode potentials, e.g. silver chloride

or saturated calomel electrode (E⁰ = + 0.246 V).

Electrode potentials E under non-standard conditions

Nernst equation

E = E0 +		RT		ln	[Aox]a
		nF
					[Ared]b

E, E⁰ el. potentials in volts

R = 8.314 l kPa K^–1 mol^–1

F = 96 500 C mol^–1

n = number of moles of electrons transferred

[A_ox] and [A_red ] relevant concentrations of reactants

After expressing R, T (298 K), and F in numbers and transposing natural logarithm into decadic (ln x = 2.3 log x), the equation will take the form

	0.059		[A ]a
E = E0 +		log	ox
	n
			[Ared]b

The electrode potential of half-cells at various concentrations of redox pair components can be calculated. On the contrary, the ratio of both redox pair components can be estimated from the measured values of electrode potentials.