Belousov-Zhabotinsky reaction
Encyclopedia
A Belousov–Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of non-equilibrium thermodynamics
, resulting in the establishment of a nonlinear chemical oscillator
. The only common element in these oscillating systems is the inclusion of bromine and an acid. The reactions are theoretically important in that they show that chemical reactions do not have to be dominated by equilibrium thermodynamic
behavior. These reactions are far from equilibrium and remain so for a significant length of time. In this sense, they provide an interesting chemical model of nonequilibrium biological phenomena, and the mathematical models of the BZ reactions themselves are of theoretical interest.
An essential aspect of the BZ reaction is its so called "excitability" — under the influence of stimuli, patterns develop in what would otherwise be a perfectly quiescent medium. Some clock reactions such as Briggs–Rauscher and BZ using the tris(bipyridine)ruthenium(II) chloride
as catalyst can be excited into self-organising activity through the influence of light.
, cerium(IV) sulfate
, propanedioic acid and citric acid
in dilute sulfuric acid
, the ratio of concentration of the cerium(IV) and cerium(III) ions oscillated, causing the colour of the solution to oscillate between a yellow solution and a colorless solution. This is due to the cerium(IV) ions being reduced by propanedioic acid to cerium(III) ions, which are then oxidized back to cerium(IV) ions by bromate(V) ions.
Belousov made two attempts to publish his finding, but was rejected on the grounds that he could not explain his results to the satisfaction of the editors of the journals to which he submitted his results. His work was finally published in a less respectable, non-reviewed journal.
Later, in 1961, a graduate student named Anatol Zhabotinsky
rediscovered this reaction sequence; however, the results of these men's work were still not widely disseminated, and were not known in the West until a conference in Prague
in 1968.
There are a number of BZ cocktails available in the chemical literature and on the web. Ferroin
, a complex
of phenanthroline
and iron
is a common indicator
. These reactions, if carried out in petri dish
es, result in the formation first of colored spots. These spots grow into a series of expanding concentric rings or perhaps expanding spirals similar to the patterns generated by a cyclic cellular automaton. The colors disappear if the dishes are shaken, and then reappear. The waves continue until the reagents are consumed. The reaction can also be performed in a beaker
using a magnetic stirrer
.
Andrew Adamatzky, a computer scientist in the University of the West of England
reported on liquid logic gates using the BZ reaction.
Investigators are also exploring the creation of a "wet computer", using self-creating "cells" and other techniques to mimic certain properties of neuron
s.
Non-equilibrium thermodynamics
Non-equilibrium thermodynamics is a branch of thermodynamics that deals with systems that are not in thermodynamic equilibrium. Most systems found in nature are not in thermodynamic equilibrium; for they are changing or can be triggered to change over time, and are continuously and discontinuously...
, resulting in the establishment of a nonlinear chemical oscillator
Chemical clock
A chemical clock is a complex mixture of reacting chemical compounds in which the concentration of one or more components exhibits periodic changes....
. The only common element in these oscillating systems is the inclusion of bromine and an acid. The reactions are theoretically important in that they show that chemical reactions do not have to be dominated by equilibrium thermodynamic
Equilibrium thermodynamics
Equilibrium Thermodynamics is the systematic study of transformations of matter and energy in systems as they approach equilibrium. The word equilibrium implies a state of balance. Equilibrium thermodynamics, in origins, derives from analysis of the Carnot cycle. Here, typically a system, as...
behavior. These reactions are far from equilibrium and remain so for a significant length of time. In this sense, they provide an interesting chemical model of nonequilibrium biological phenomena, and the mathematical models of the BZ reactions themselves are of theoretical interest.
An essential aspect of the BZ reaction is its so called "excitability" — under the influence of stimuli, patterns develop in what would otherwise be a perfectly quiescent medium. Some clock reactions such as Briggs–Rauscher and BZ using the tris(bipyridine)ruthenium(II) chloride
Tris(bipyridine)ruthenium(II) chloride
Trisruthenium dichloride is the coordination compound with the formula [Ru3]Cl2. This red crystalline salt is obtained as the hexahydrate, although all of the properties of interest are in the cation [Ru3]2+, which has received much attention because of its distinctive optical properties...
as catalyst can be excited into self-organising activity through the influence of light.
History
The discovery of the phenomenon is credited to Boris Belousov. He noted, sometime in the 1950s (various sources' date ranges from 1951 to 1958), that in a mix of potassium bromatePotassium bromate
Potassium bromate , is a bromate of potassium and takes the form of white crystals or powder.-Uses in baking:Potassium bromate is typically used as a flour improver , strengthening the dough and allowing higher rising. It is an oxidizing agent, and under the right conditions, will be completely...
, cerium(IV) sulfate
Cerium(IV) sulfate
Cerium sulfate, also called ceric sulfate, is a yellow to yellow/orange chemical compound. It exists as the anhydrous salt Ce2; a few hydrated forms are also known: Ce2 ⋅ xH2O, with x equal to 4, 8, or 12. Ceric sulfate is available commercially.-Properties:Ceric sulfate is moderately soluble in...
, propanedioic acid and citric acid
Citric acid
Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
in dilute sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
, the ratio of concentration of the cerium(IV) and cerium(III) ions oscillated, causing the colour of the solution to oscillate between a yellow solution and a colorless solution. This is due to the cerium(IV) ions being reduced by propanedioic acid to cerium(III) ions, which are then oxidized back to cerium(IV) ions by bromate(V) ions.
Belousov made two attempts to publish his finding, but was rejected on the grounds that he could not explain his results to the satisfaction of the editors of the journals to which he submitted his results. His work was finally published in a less respectable, non-reviewed journal.
Later, in 1961, a graduate student named Anatol Zhabotinsky
Anatol Zhabotinsky
Anatoly Markovich Zhabotinsky created a theory of the Belousov-Zhabotinsky reaction in the 1960s and published a comprehensive body of experimental data on chemical wave propagation and pattern formation in nonuniform media...
rediscovered this reaction sequence; however, the results of these men's work were still not widely disseminated, and were not known in the West until a conference in Prague
Prague
Prague is the capital and largest city of the Czech Republic. Situated in the north-west of the country on the Vltava river, the city is home to about 1.3 million people, while its metropolitan area is estimated to have a population of over 2.3 million...
in 1968.
There are a number of BZ cocktails available in the chemical literature and on the web. Ferroin
Ferroin
Ferroin is the chemical compound with the formula [Fe3]SO4, where o-phen is an abbreviation for 1,10-phenanthroline, a bidentate ligand. The term "ferroin" is used loosely and includes salts of other anions such as chloride.-Redox indicator:...
, a complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
of phenanthroline
Phenanthroline
Phenanthroline is a heterocyclic organic compound. As a bidentate ligand in coordination chemistry, it forms strong complexes with most metal ions...
and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
is a common indicator
Redox indicator
A redox indicator is an indicator that undergoes a definite color change at a specific electrode potential....
. These reactions, if carried out in petri dish
Petri dish
A Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...
es, result in the formation first of colored spots. These spots grow into a series of expanding concentric rings or perhaps expanding spirals similar to the patterns generated by a cyclic cellular automaton. The colors disappear if the dishes are shaken, and then reappear. The waves continue until the reagents are consumed. The reaction can also be performed in a beaker
Beaker (glassware)
A beaker is a simple container for stirring, mixing and heating liquids commonly used in many laboratories. Beakers are generally cylindrical in shape, with a flat bottom. Most also have a small spout to aid pouring as shown in the picture...
using a magnetic stirrer
Magnetic stirrer
A magnetic stirrer or magnetic mixer is a laboratory device that employs a rotating magnetic field to cause a stir bar immersed in a liquid to spin very quickly, thus stirring it. The rotating field may be created either by a rotating magnet or a set of stationary electromagnets, placed beneath...
.
Andrew Adamatzky, a computer scientist in the University of the West of England
University of the West of England
The University of the West of England is a university based in the English city of Bristol. Its main campus is at Frenchay, about five miles north of the city centre...
reported on liquid logic gates using the BZ reaction.
Investigators are also exploring the creation of a "wet computer", using self-creating "cells" and other techniques to mimic certain properties of neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s.
See also
- Excitable mediumExcitable mediumAn excitable medium is a nonlinear dynamical system which has the capacity to propagate a wave of some description, and which cannot support the passing of another wave until a certain amount of time has passed ....
- Briggs–Rauscher reaction
External links
- Interactive Science Experiment Showcasing the BZ Reaction (A-Level)
- A Survey Article on the Mathematics of the BZ Reaction
- The Scholarpedia article on the Belousov-Zhabotinsky reaction
- The Belousov–Zhabotinski Reaction
- The Belousov–Zhabotinsky Reaction
- The Phenomenology of the Belousov–Zhabotinsky Reaction, with pictures
- Video of BZ reaction
- The Belousov–Zhabotinski Reaction PDF file
- Paper cargo surfs chemical waves — Oscillating chemical waves induced by BZ reactions can propel small objects, New Scientist, 18 February 2008
- The home page of Anatol M. Zhabotinsky