Electrolysis and User talk:69.115.162.176: Difference between pages

Revision as of 03:37, 28 October 2005

Revision as of 07:06, 21 November 2005

Line 1:

{{test-n|Matter}}

:''This article is about the chemical process. [[Electrology|Electrolysis]] is also a method of [[epilation]].''

-->--

{{test-n|Brownian motion}}

In chemistry and manufacturing, '''electrolysis''' is a method of separating bonded [[chemical element|element]]s and [[chemical compound|compound]]s by passing an [[electric current]] through them. The most common form of electrolysis is electrolysis of water:

:2H<sub>2<sub>O<sub>(l)<sub> &rarr; 2H<sub>2(g)<sub> + O<sub>2(g)<sub>

== Overview ==

An ionic compound is dissolved with an appropriate [[solvent]], or otherwise melted by heat, so that its [[ion]]s are available in the liquid. An electrical current is applied between a pair of metal [[electrode]]s immersed in the liquid. The negatively charged electrode is called the [[cathode]], and the positively charged one the [[anode]].

<!--

Many people misunderstand these definitions and think they should be the other way round. Please read the [[electrode]] article before trying to 'correct' them.

-->

Each electrode attracts ions which are of the opposite [[Electric charge|charge]]. Therefore, positively charged ions (called [[cation]]s) move towards the cathode, while negatively charged ions (termed [[anion]]s) move toward the anode. The energy required to separate the ions, and cause them to gather at the respective electrodes, is provided by an electrical power supply. At the probes, [[electron]]s are absorbed or released by the ions, forming a collection of the desired element or compound. For example, when [[water (molecule)|water]] is electrolyzed, [[hydrogen]] gas (H₂) bubbles at the cathode, and [[oxygen]] gas (O₂) rises at the anode. This effect was first discovered by [[William Nicholson (chemist)|William Nicholson]], an English chemist, in [[1800]].

The amount of electrical energy that must be added equals the change in [[Gibbs free energy]] of the reaction plus the losses in the system. The losses can (theoretically) be arbitrarily close to zero, so the maximum [[thermodynamics|thermodynamic]] efficiency equals the [[enthalpy]] change divided by the free energy change of the reaction. In most cases the electric input is larger than the enthalpy change of the reaction, so some energy is released in the form of heat. In some cases, for instance in the electrolysis of [[steam]] into hydrogen and oxygen at high temperature, the opposite is true. Heat is absorbed from the surroundings, and the [[heating value]] of the produced hydrogen is higher than the electric input. In this case the efficiency can be said to be greater than 100%. (It is worth noting that the maximum theoretic efficiency of a [[fuel cell]] is the inverse of that of electrolysis. It is thus impossible to create a [[perpetual motion]] machine by combining the two processes. See [[water fuel cell]] for an example of such an attempt.)

The following technologies are related to electrolysis:

* [[Electrochemical cell]]s, including the hydrogen [[fuel cell]], use the reverse of this process.

* [[Gel electrophoresis]] is an electrolysis where the solvent is a gel: it is used to separate substances, such as [[DNA]] strands, based on their electrical charge.

== Experimenters ==

Scientific pioneers of electrolysis included:

*[[Humphry Davy]]

*[[Michael Faraday]]

*[[Paul Heroult|Paul Héroult]]

*[[Svante Arrhenius]]

*[[Adolph Wilhelm Hermann Kolbe]]

More recently, electrolysis of [[heavy water]] was performed by Fleischmann and Pons in [[Fleischmann-Pons experiment|their famous experiment]], resulting in anomalous heat generation and the controversial claim of [[cold fusion]].

==First law of electrolysis==

In [[1832]], [[Michael Faraday]] reported that the quantity of elements separated by passing an electrical current through a molten or dissolved [[salt]] was proportional to the quantity of current passed through the circuit. This became the basis of [[Faraday's law of electrolysis|the first law of electrolysis]].

==Second law of electrolysis==

Faraday also discovered that the [[mass]] of the resulting separated elements was directly proportional to the [[atomic mass]]es of the elements when an appropriate integral divisor was applied. This provided strong evidence that discrete particles of electricity existed as parts of the atoms of elements.

== Industrial uses ==

*Manufacture of [[aluminium]], [[lithium]], [[aspirin]].

*Manufacture of [[hydrogen]] for [[hydrogen car]]s and [[fuel cell]]s.

*[[High-temperature electrolysis]] is also being used for this.

*[[Coulometry|Coulometric]] techniques can be used to determine the amount of matter transformed during electrolysis by measuring the amount of electricity required to perform the electrolysis.

== Domestic uses ==

[[Chlorine]] and [[sodium hydroxide]] are extracted from [[sodium chloride]] [[brine]] by electrolysis. Chlorine is, among many things, used as a [[disinfectant]] and for [[bleach]]ing. [[Sodium hydroxide]], or [[lye]], is a [[strong base]] that is commonly used in [[drain cleaner]]s.

[[Category:Electrochemistry]]

[[Category:Chemical processes]]

[[Category:Electrolysis|*]]

[[Category:Industrial processes]]

[[ca:Electròlisi]]

[[cs:Elektrolýza]]

[[da:Elektrolyse]]

[[de:Elektrolyse]]

[[el:Ηλεκτρόλυση]]

[[es:Electrólisis]]

[[fr:Électrolyse]]

[[gl:Electrólise]]

[[ko:전기분해]]

[[io:Elektrolizo]]

[[id:Elektrolisis]]

[[it:Elettrolisi]]

[[he:אלקטרוליזה]]

[[nl:Elektrolyse]]

[[nds:Elektrolyse]]

[[ja:電気分解]]

[[no:Elektrolyse]]

[[pl:Elektroliza]]

[[pt:Eletrólise]]

[[ru:Электролиз]]

[[sl:Elektroliza]]

[[fi:Elektrolyysi]]

[[tr:Elektroliz]]