dissociation
American Heritage Dictionary:
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dis·so·ci·a·tion
(dĭ-sō'sē-ā'shən, -shē-) 
n.
n.
- The act of dissociating or the condition of having been dissociated.
- Chemistry.
- The process by which the action of a solvent or a change in physical condition, as in pressure or temperature, causes a molecule to split into simpler groups of atoms, single atoms, or ions.
- The separation of an electrolyte into ions of opposite charge.
- Psychiatry. A psychological defense mechanism in which specific, anxiety-provoking thoughts, emotions, or physical sensations are separated from the rest of the psyche.
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dissociation
Oxford Dictionary of Chemistry:
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dissociation
The breakdown of a molecule, ion, etc., into smaller molecules, ions, etc. An example of dissociation is the reversible reaction of hydrogen iodide at high temperatures
2HI(g) ⇌ H2(g)+I2(g)
The equilibrium constant of a reversible dissociation is called the dissociation constant. The term 'dissociation' is also applied to ionization reactions of acids and bases in water; for example HCN+H2O ⇌ H3O++CN−
which is often regarded as a straightforward dissociation into ions HCN ⇌ H++CN−
The equilibrium constant of such a dissociation is called the acid dissociation constant or acidity constant, given by Ka = [H+][A−]/[HA]
for an acid HA (the concentration of water [H2O] can be taken as constant). Ka is a measure of the strength of the acid. Similarly, for a nitrogenous base B, the equilibrium B+H2O ⇌ BH++OH−
is also a dissociation; with the base dissociation constant, or basicity constant, given by Kb = [BH+][OH−]/[B]
For a hydroxide MOH,Kb = [M+][OH−]/[MOH]
Britannica Concise Encyclopedia:
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dissociation
Breaking of a chemical compound into simpler constituents as a result of added energy, as in the case of gaseous molecules dissociated by heating; also, the effect of a solvent on a dissolved polar compound (electrolyte), as in the case of an inorganic salt, such as sodium chloride, dissolved in water. All electrolytes dissociate into ions to a greater or lesser extent in polar solvents (in which the molecules are electric dipoles). The degree of dissociation can be used to determine the equilibrium constant. Dissociation is used to explain electrical conductivity and many other properties of electrolytic solutions.
For more information on dissociation, visit Britannica.com.
Antonyms by Answers.com:
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dissociation
n
Definition: detachment, separation
Antonyms: association, attachment, connection, union
Oxford Dictionary of Sports Science & Medicine:
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dissociation
An attentional style characterized by distraction. Dissociation is exhibited by athletes who are unaware of their surroundings because they are mentally absorbed thinking about other things while participating in their sport. Compare association.
Columbia Encyclopedia:
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dissociation
dissociation, in chemistry, separation of a substance into atoms or ions. Thermal dissociation occurs at high temperatures. For example, hydrogen molecules (H2) dissociate into atoms (H) at very high temperatures; at 5,000°K about 95% of the molecules in a sample of hydrogen are dissociated into atoms. Electrolytic dissociation occurs when an electrolyte is dissolved in a polar solvent. For example, when hydrogen chloride, HCl, is dissolved in water to form hydrochloric acid, most of its molecules dissociate into hydrogen ions (H+) and chloride ions (Cl−). Some pure substances spontaneously dissociate. For example, in pure water some of the molecules dissociate to form hydrogen ions and hydroxyl ions. Dissociation is generally reversible; when the atoms or ions of the dissociated substance are returned to the original conditions, they recombine in the original form of the substance. The dissociation constant is a measure of the extent of dissociation. It is represented by the symbol K. In the simplest case, if a substance AB dissociates into two parts A and B and the concentrations of AB, A, and B are represented by [AB], [A], and [B], then K=[A]×[B]/[AB]. The dissociation constant is measured at equilibrium, and its value is usually affected by changes in temperature.
Oxford Dictionary of Biochemistry:
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dissociation
- or disassociation a reversible splitting of a chemical substance into simpler entities; compare association. In this sense, the term may be applied to:
(a) the heterolysis of a covalent bond, yielding, in the case of an initially uncharged molecule, positively and negatively charged ions: ionic dissociation;
(b) the disaggregation of a macromolecular homopolymer or heteropolymer into its constituent units (i.e. protomers), usually by a stepwise process through components of intermediate size (i.e. oligomers) and without rupture of covalent bonds;
(c) the breakdown of an enzyme-substrate complex, which may or may not involve cleavage of a covalent bond; or
(d) the separation of a complex of two or more molecules into the constituent molecules. - a splitting of a chemical substance by the homolysis of a covalent bond, yielding radicals.
- translocation between a large chromosome and a small supernumerary one, in effect splitting the large chromosome into two chromosomes.
- separation (induced or spontaneous) of the nuclear components of a heterokaryotic dikaryon.
| dissimilation, disproportionation, displacement reaction | |
| dissociation constant, dissociation energy, distal |
Saunders Veterinary Dictionary:
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dissociation
The act of separating or the state of being separated.
- atrial d. — independent beating of the left and right atria, each with normal rhythm or with various combinations of normal rhythm, atrial flutter or atrial fibrillation.
- atrioventricular d. — independent pacemakers in the atria and ventricles.
- d. constant — the tendency of a solute to dissociate in solution.
- hepatocyte d. — hepatocytes becomes detached from their neighboring cells, either generally or locally; a feature of death of the patient.
Mosby's Dental Dictionary:
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dissociation
n
The psychologically induced, distinct partition of separate mental functions (e.g., identity, memory, and awareness) from normal behavior or consciousness.
Random House Word Menu:
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categories related to 'dissociation'
- Chemical Properties and Reactions - dissociation: breakdown of molecule or other group of atoms into smaller groups of atoms or ions
Wikipedia on Answers.com:
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Dissociation
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Look up dissociation in Wiktionary, the free dictionary. |
Dissociation (in the wide sense of the word) is an act of disuniting or separating a complex object into parts.
- Dissociation (chemistry), general process in which ionic compounds (complexes, or salts) split into smaller particles, usually in a reversible manner
- Dissociation (neuropsychology), identification of the neural substrate of a particular brain function through various methods
- Dissociation (psychology), altered state of consciousness characterized by partial or complete disruption of the normal integration of a person’s normal conscious or psychological functioning
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This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article. |
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American Heritage Dictionary
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
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Oxford Dictionary of Chemistry
A Dictionary of Chemistry. Sixth Edition. Copyright © Market House Books Ltd, 2008. All rights reserved.
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Britannica Concise Encyclopedia
Britannica Concise Encyclopedia. © 1994-2012 Encyclopædia Britannica, Inc. All rights reserved. Read more
Oxford Dictionary of Sports Science & Medicine
The Oxford Dictionary of Sports Science & Medicine. Copyright © Michael Kent 1998, 2006, 2007. All rights reserved.
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Columbia Encyclopedia
The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2012, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/.
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Oxford Dictionary of Biochemistry
Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved.
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Saunders Veterinary Dictionary
Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.
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Mosby's Dental Dictionary
Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.
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Random House Word Menu
© 2010 Write Brothers Inc. Word Menu is a registered trademark of the Estate of Stephen Glazier.
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