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Encyclopedia > Electrolysis

In chemistry and manufacturing, electrolysis is a method of separating chemically bonded elements and compounds by passing an electric current through them. A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... Look up chemical compound in Wiktionary, the free dictionary. ... Electric current is the flow (movement) of electric charge. ...

Contents

Overview

Electrolysis involves the passage of an electric current through a typically ionic substance which is either molten or dissolved in an aqueous solution resulting in chemical reactions at the electrodes. The positive electrode is called the anode, and the negative is the cathode. Electric current is the flow (movement) of electric charge. ... From ancient Greece (Ionic) An Ionian is a member of one of the four great divisions of the ancient Greek people. ...


An ionic compound is dissolved with an appropriate solvent, or melted by heat, so that its ions are available in the liquid. An electrical current is applied between a pair of inert electrodes immersed in the liquid. The negatively charged electrode is called the cathode, and the positively charged one the anode. Each electrode attracts ions which are of the opposite charge. Therefore, positively charged ions (called cations) move towards the cathode, while negatively charged ions (termed anions) 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, electrons are absorbed or released by the ions, forming a collection of the desired element or compound. The crystal structure of sodium chloride, NaCl, a typical ionic compound. ... For other uses, see Solvent (disambiguation). ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... This article is about the electrically charged particle. ... In English, to be inert is to be in a state of doing little or nothing. ... For other uses, see Electrode (disambiguation). ... Diagram of a copper cathode in a Daniells cell. ... Diagram of a zinc anode in a galvanic cell. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... A cation is an ion with positive charge. ... An anion is an ion with negative charge. ... For other uses, see Electron (disambiguation). ...


Oxidation of anions can take place at the anode, and the reduction of cations at the cathode. For example, it is possible to oxidize cations at the anode: The most fundamental reactions in chemistry are the redox processes. ... An anion is an ion with negative charge. ... Diagram of a zinc anode in a galvanic cell. ... Reduction or reducing has several meanings: In mathematics, reduction is the process of manipulating a series of equations or matrices into a desired simpler format. ... A cation is an ion with positive charge. ... Diagram of a copper cathode in a Daniells cell. ... A cation is an ion with positive charge. ... Diagram of a zinc anode in a galvanic cell. ...

mathrm{Fe^{2+}_{aq} longrightarrow  Fe^{3+}_{aq} +  e^- } .

It is also possible to reduce anions at the cathode: An anion is an ion with negative charge. ... Diagram of a copper cathode in a Daniells cell. ...

mathrm{Fe(CN)_6^{3-} +  e^- longrightarrow  Fe(CN)_6^{4-} } .

Neutral molecules can also react at either electrode. For example:


mathrm{+  2 e^- +  2 H^+ longrightarrow  } Image:Hydroquinone.svg Image File history File links P-Benzoquinone. ... Image File history File links No higher resolution available. ...


In electrolysis, the anode is the positive electrode, meaning it has a deficit of electrons; species in contact with the anode can be stripped of electrons (i.e., they are oxidized). The cathode is the negative electrode, meaning it has a surplus of electrons. Species in contact with the cathode tend to gain electrons (i.e., they are reduced).


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 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. (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.) In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ... Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dynamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ... For other uses, see Steam (disambiguation). ... Heating value (or calorific value) is used to define the amount of heat released during the combustion of a fuel or food. ... A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... This article or section should include material from Parallel Path See also Perpetuum mobile as a musical term Perpetual motion machines (the Latin term perpetuum mobile is not uncommon) are a class of hypothetical machines which would produce useful energy in a way science cannot explain (yet). ... The water fuel cell, named by American Stanley Meyer, is a device designed to convert water into its component elements, hydrogen and oxygen (2H2O → 2H2 + O2). ...


A higher current flow (amperage) through the cell means it will be passing more electrons through it at any given time. This means a faster rate of reduction at the cathode and a faster rate of oxidation at the anode. This corresponds to a greater number of moles of product. The amount of current that passes depends on the conductance of the electrodes and electrolyte, though it also depends on how much current the power source itself can generate.


Current also makes a difference in that it can shift chemical equilibria by sheer mass action. The processes in an electrolytic cell with just two or three reactants can become very complex. Most of the time it is best to search the literature to see what current density works best for a desired process. For instance, metals plated at a certain current density might form a durable and shiny coating on the substrate, while some other current density might form an excessively grainy, dull coating.


A higher potential difference (voltage) applied to the cell means the cathode will have more energy to bring about reduction, and the anode will have more energy to bring about oxidation. Higher potential difference enables the electrolytic cell to oxidize and reduce energetically more "difficult" compounds. This can drastically change what products will form in a given experiment. On a practical level, both current and voltage determine what will form in a cell.


The following technologies are related to electrolysis:

A demonstration electrochemical cell setup resembling the Daniell cell. ... A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... Gel electrophoresis is a technique used for the separation of deoxyribonucleic acid, ribonucleic acid, or protein molecules through an electric charge. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ...

Electrolysis of water

Hoffman electrolysis apparatus used in electrolysis of water
Main article: Electrolysis of water

One important use of electrolysis of water is to produce hydrogen. Image File history File links Hoffman_voltameter. ... Image File history File links Hoffman_voltameter. ... Hoffman voltameter used to electrolyze water. ...

2H2O(l) → 2H2(g) + O2(g)

This has been suggested as a way of shifting society toward using hydrogen as an energy carrier for powering electric motors and internal combustion engines. (See hydrogen economy.) An energy carrier is simply any system or substance used to transfer energy from somewhere to somewhere else. ... A hydrogen economy is a hypothetical economy in which the energy needed for motive power (for automobiles or other vehicle types) or electricity (for stationary applications) is derived from reacting hydrogen (H2) with oxygen. ...


Electrolysis of water can be observed by passing direct current from a battery or other DC power supply through a cup of water (in practice a saltwater solution increases the reaction intensity making it easier to observe). Using platinum electrodes, hydrogen gas will be seen to bubble up at the cathode, and oxygen will bubble at the anode. If other metals are used as the anode, there is a chance that the oxygen will react with the anode instead of being released as a gas. For example using iron electrodes in a sodium chloride solution electrolyte, iron oxide will be produced at the anode, which will react to form iron hydroxide. When producing large quantities of hydrogen, this can significantly contaminate the electrolytic cell - which is why iron is not used for commercial electrolysis. Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... Diagram of a copper cathode in a Daniells cell. ... Diagram of a zinc anode in a galvanic cell. ...


The energy efficiency of water electrolysis varies widely. The efficiency is a measure of what fraction of electrical energy used is actually contained within the hydrogen. Some of the electrical energy is converted to heat, a useless by-product. Some reports quote efficiencies between 50 and 70%[1] This efficiency is based on the Lower Heating Value of Hydrogen. The Lower Heating Value of Hydrogen is thermal energy released when Hydrogen is combusted. This does not represent the total amount of energy within the Hydrogen, hence the efficiency is lower than a more strict definition. Other reports quote the theoretical maximum efficiency of electrolysis. The theoretical maximum efficiency is between 80 and 94%.[2]. The theoretical maximum considers the total amount of energy absorbed by both the hydrogen and oxygen. These values only refer to the efficiency of converting electrical energy into hydrogen's chemical energy. The energy lost in generating the electricity is not included. For instance, when considering a power plant that converts the heat of nuclear reactions into hydrogen via electrolysis, the total efficiency is more like 25–40%.[3] In physics and engineering, including mechanical and electrical engineering, energy efficiency is a dimensionless number, with a value between 0 and 1 or, when multiplied by 100, is given as a percentage. ... A nuclear power station. ...


About four percent of hydrogen gas produced worldwide is created by electrolysis, and normally used onsite. Hydrogen is used for the creation of ammonia for fertilizer via the Haber process, and converting heavy petroleum sources to lighter fractions via hydrocracking. There is some speculation about future development of hydrogen as an energy carrier. The Haber Process (also known as Haber–Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ... In petroleum geology and chemistry, cracking is the process whereby complex organic molecules (e. ...


Experimenters

Scientific pioneers of electrolysis included:

More recently, electrolysis of heavy water was performed by Fleischmann and Pons in their famous experiment, allegedly resulting in anomalous heat generation and the controversial claim of cold fusion. Sir Humphry Davy, 1st Baronet, FRS (17 December 1778 – 29 May 1829) was a British chemist and physicist. ... Michael Faraday, FRS (September 22, 1791 – August 25, 1867) was an English chemist and physicist (or natural philosopher, in the terminology of that time) who contributed to the fields of electromagnetism and electrochemistry. ... The French scientist Paul (Louis-Toussaint) Héroult (1863-1914) was the inventor of the aluminium electrolysis and of the electric steel furnace. ... Svante August Arrhenius (February 19, 1859 – October 2, 1927) was a Swedish chemist and one of the founders of the science of physical chemistry. ... Adolph Wilhelm Hermann Kolbe (September 27, 1818 – November 25, 1884) was a chemist. ... There have been several well-known people named William Nicholson, including: William Nicholson (artist) William Nicholson (chemist) William Nicholson (dramatist) William Nicholson (Mayor of Melbourne) Sir William Nicholson (soldier), British General, and Chief of the Imperial General Staff William Nicholson (naval officer) served in the United States Navy. ... Joseph Louis Gay-Lussac. ... An 1859 portrait of Alexander von Humboldt by the artist Julius Schrader, showing Mount Chimborazo in the background. ... Heavy water is dideuterium oxide, or D2O or 2H2O. It is chemically the same as normal water, H2O, but the hydrogen atoms are of the heavy isotope deuterium, in which the nucleus contains a neutron in addition to the proton found in the nucleus of any hydrogen atom. ... This article is about the nuclear reaction. ... This article is about the nuclear reaction. ...


Faraday's laws of electrolysis

See Also: Faraday's laws of electrolysis Faraday studied the process of electrolysis in detail. ...


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 electric charge passed through the circuit. This became the basis of the first law of electrolysis. Year 1832 (MDCCCXXXII) was a leap year starting on Sunday (link will display the full calendar) of the Gregorian Calendar (or a leap year starting on Friday of the 12-day slower Julian calendar). ... Michael Faraday, FRS (September 22, 1791 – August 25, 1867) was an English chemist and physicist (or natural philosopher, in the terminology of that time) who contributed to the fields of electromagnetism and electrochemistry. ... For other uses, see Salt (disambiguation). ...


Second law of electrolysis

Faraday also discovered that the mass of the resulting separated elements was directly proportional to the atomic masses of the elements when an appropriate integral divisor was applied. This provided strong evidence that discrete particles of matter existed as parts of the atoms of elements. For other uses, see Mass (disambiguation). ... The atomic mass (ma) is the mass of an atom at rest, most often expressed in unified atomic mass units. ...


Industrial uses

Electrolysis has many other uses: Aluminum redirects here. ... This article is about the chemical element named Lithium. ... For sodium in the diet, see Edible salt. ... General Name, symbol, number potassium, K, 19 Chemical series alkali metals Group, period, block 1, 4, s Appearance silvery white Standard atomic weight 39. ... This article is about the chemistry of hydrogen. ... It has been suggested that this article or section be merged with Hydrogen vehicle. ... A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... High-temperature electrolysis schema. ... Coulometry is the name given to a group of electroanalytical chemistry techniques that determine the amount of matter transformed during an electrolysis reaction by measuring the amount of electricity (in coulombs) consumed or produced. ... General Name, symbol, number chlorine, Cl, 17 Chemical series halogens Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... Flash point Non-flammable. ... Sodium chlorate (NaClO3) is an oxidizing agent. ... Potassium chlorate is a compound containing potassium, chlorine and oxygen, with the chemical formula K[ClO3]. In pure form, it is a white crystalline substance. ... Trifluoroacetic acid (TFA) is a strong, hygroscopic, non-oxidizing, organic acid with a molecular formula C2HF3O2. ...

  • Electrometallurgy is the process of reduction of metals from metallic compounds to obtain the pure form of metal using electrolysis. For example: sodium hydroxide in its molten form is separated by electrolysis into sodium and oxygen, both of which have important chemical uses. (Water is produced at the same time.)
  • Anodization is an electrolytic process that makes the surface of metals resistant to corrosion. For example, ships are saved from being corroded by oxygen in the water by this process. The process is also used to decorate surfaces.
  • A battery works by the reverse process to electrolysis. Humphry Davy found that lithium acts as an electrolyte and provides electrical energy.
  • Production of oxygen in spacecraft. The oxygen that astronauts breathe in space is produced by electrolysis of water, using solar panels as a source of electrical energy.[citation needed]
  • Electroplating is used in layering metals to fortify them. Electroplating is used in many industries for functional or decorative purposes, as in vehicle bodies and nickel coins.
  • Production of hydrogen for fuel, using a cheap source of electrical energy.
  • Electrolytic Etching of metal surfaces like tools or knives with a permanent mark or logo.

Hydrometallurgy is part of the field of extractive metallurgy involving the use of aqueous chemistry for the recovery of metals from ores, concentrates, and recycled or residual materials. ... Anodising is a process used to protect aluminium from corrosion. ... For the hazard, see corrosive. ... Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams. ... Sir Humphry Davy, 1st Baronet, FRS (17 December 1778 – 29 May 1829) was a British chemist and physicist. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... The Space Shuttle Discovery as seen from the International Space Station. ... Electroplating is the process of using Davd lloyd current to coat an electrically conductive object with a relatively thin layer of metal. ...

See also

Look up electrolysis in
Wiktionary, the free dictionary.

  Results from FactBites:
 
Electrolysis - Wikipedia, the free encyclopedia (1374 words)
In some cases, for instance in the electrolysis of steam into hydrogen and oxygen at high temperature, the opposite is true.
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.
More recently, electrolysis of heavy water was performed by Fleischmann and Pons in their famous experiment, resulting in anomalous heat generation and the controversial claim of cold fusion.
Electrolysis of water - Wikipedia, the free encyclopedia (840 words)
Electrolysis of water is an electrolytic process which decomposes water into oxygen and hydrogen gas with the aid of an electric current, where a power source from a 6 volt battery is commonly used.
The electrolysis cell consists of two electrodes (usually an inert metal such as platinum) submerged in an electrolyte and connected to opposite poles of a source of direct current.
High-temperature electrolysis (also HTE or steam electrolysis) is a method currently being investigated for water electrolysis with a heat engine.
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