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Its absolute electrode potential is estimated to be 4.44 ± 0.02 V [1] at 25 °C, but to form a basis for comparison with all other electrochemical reactions, hydrogen's standard electrode potential (E°) is declared to be zero volts at any temperature. [2]
The data below tabulates standard electrode potentials (E°), in volts relative to the standard hydrogen electrode (SHE), at: Temperature 298.15 K (25.00 °C; 77.00 °F); Effective concentration (activity) 1 mol/L for each aqueous or amalgamated (mercury-alloyed) species; Unit activity for each solvent and pure solid or liquid species; and
In electrochemistry, electrode potential is the voltage of a galvanic cell built from a standard reference electrode and another electrode to be characterized. [1] By convention, the reference electrode is the standard hydrogen electrode (SHE). It is defined to have a potential of zero volts. It may also be defined as the potential difference ...
However, the potential of a reference electrode, standard hydrogen electrode (SHE), is defined as to 0.00 V. An electrode with unknown electrode potential can be paired with either the standard hydrogen electrode, or another electrode whose potential has already been measured, to determine its "absolute" potential.
Common reference electrodes and potential with respect to the standard hydrogen electrode (SHE): Standard hydrogen electrode (SHE) (E = 0.000 V) activity of H + = 1 Molar; Normal hydrogen electrode (NHE) (E ≈ 0.000 V) concentration H + = 1 Molar; Reversible hydrogen electrode (RHE) (E = 0.000 V - 0.0591 × pH) at 25 °C
This method of calibration avoids the need to know the standard electrode potential. The proportionality constant, 1/z, is ideally equal to , the "Nernstian slope". In practice, a glass electrode is used instead of the cumbersome hydrogen electrode. A combined glass electrode has an in-built reference electrode.
A reversible hydrogen electrode (RHE) is a reference electrode, more specifically a subtype of the standard hydrogen electrodes, for electrochemical processes. Unlike the standard hydrogen electrode, its measured potential does change with the pH, so it can be directly used in the electrolyte. [1] [2] [3]
Absolute electrode potential, in electrochemistry, according to an IUPAC definition, [1] is the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).