WordNet

partially or to the extent of a half; "he was half hidden by the bushes"
one of two divisions into which some games or performances are divided: the two divisions are separated by an interval
(of siblings) related through one parent only; "a half brother"; "half sister"
consisting of one of two equivalent parts in value or quantity; "a half chicken"; "lasted a half hour"
partial; "gave me a half smile"; "he did only a half job"
small room in which a monk or nun lives (同)cubicle
a device that delivers an electric current as the result of a chemical reaction (同)electric cell
a room where a prisoner is kept (同)jail cell, prison cell
(biology) the basic structural and functional unit of all organisms; they may exist as independent units of life (as in monads) or may form colonies or tissues as in higher plants and animals
any small compartment; "the cells of a honeycomb"
a small unit serving as part of or as the nucleus of a larger political movement (同)cadre

PrepTutorEJDIC

〈C〉〈U〉『半分』,2分の1;約半分 / 〈U〉《時刻を表す数詞と共に用いて》『半』,30分 / 〈C〉《おもに英》(2学期制の学校での)前(後)期 / 〈C〉(競技などの)前(後)半;(野球で1イニングの)表(裏) / 〈C〉=halfback / 『半分の』 / 不十分な,中途はんぱな / 『半ば』,半分[だけ] / 半時間だけ,30分だけ / 不完全に / かなり,ほとんど
(刑務所の)『独房』;(修道院の)小さい独居室 / (ミツバチの)みつ房,巣穴 / 小さい部屋 / 『細胞』 / 電池 / 花粉室 / (共産党などの)細胞
おや,はああ,ああ(驚き・喜び・疑い・ためらいなどを表す声)
hectare; hectares

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/05/19 00:37:04」(JST)

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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 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

References

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

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