Half cell Information & Half cell Links at HealthHaven.com

A half cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte separated by a naturally-occurring Helmholtz double layer. Chemical reactions within this layer momentarily pump electric charges between the electrode and the electrolyte, resulting in a potential difference between the electrode and the electrolyte. The typical anode reaction involves a metal atom in the electrode being dissolved and transported as a positive ion across the double layer, causing the electrolyte to acquire a net positive charge while the electrode acquires a net negative charge. The growing potential difference creates an intense electric field within the double layer, and the potential rises in value until the field halts the net charge-pumping reactions. This self-limiting action occurs almost instantly in an isolated half cell; in applications two dissimilar half cells are appropriately connected to constitute a Galvanic cell.

A standard half cell, used in electrochemistry, consists of a metal electrode in a 1 molar (1 mol/L) aqueous solution of the metal's salt, at 298 kelvin (25 °C)^[1]. The electrochemical series, which consists of standard electrode potentials and is closely related to the reactivity series, was generated by measuring the difference in potential between the metal half cell in a circuit with a standard hydrogen half cell, connected by a salt bridge.

The standard hydrogen half cell:

2H⁺(aq) + 2e^- → H₂(g)

The half cells of a Daniell cell:

Original equation

Zn + Cu²⁺ → Zn²⁺ + Cu

Half cell (anode) of Zn

Zn → Zn²⁺ + 2e⁻

Half cell (cathode) of Cu

Cu²⁺ + 2e⁻ → Cu

[edit] References

^ Andrews, Donald H.; Richard J. Kokes (1962). "Electrochemistry". Fundamental Chemistry. New York: John Wiley & Sons, Inc.. p. 482.

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[0] Andrews, Donald H.; Richard J. Kokes (1962). "Electrochemistry". Fundamental Chemistry. New York: John Wiley & Sons, Inc.. p. 482.

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