dissociation


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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 electrolyteelectrolyte
, electrical conductor in which current is carried by ions rather than by free electrons (as in a metal). Electrolytes include water solutions of acids, bases, or salts; certain pure liquids; and molten salts.
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 is dissolved in a polar solventsolvent,
constituent of a solution that acts as a dissolving agent. In solutions of solids or gases in a liquid, the liquid is the solvent. In all other solutions (i.e., liquids in liquids or solids in solids) the constituent that is present in larger quantity is considered the
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. For example, when hydrogen chloride, HCl, is dissolved in water to form hydrochloric acid, most of its molecules dissociate into hydrogen ionsion,
atom or group of atoms having a net electric charge. Positive and Negative Electric Charges

A neutral atom or group of atoms becomes an ion by gaining or losing one or more electrons or protons.
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 (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.

Dissociation

 

the process by which molecules break up into a number of simpler particles—molecules, radicals, atoms, or ions. Three types of dissociation are generally distinguished: thermal dissociation, which takes place at elevated temperature (for example, N2O4 ⇄ 2NO2); electrolytic dissociation, which occurs when electrolytes are dissolved (the splitting of the molecules of electrolytes into ions, for example, KOH ⇄ K+ + OH-); and photochemical dissociation, which is observed under the action of light (for example, Cl2 + hγ → 2Cl, where hy is a quantum of light). A quantitative characteristic of dissociation is the degree of dissociation, which is the ratio of the number of molecules that have broken up to the total number of molecules.

dissociation

[də‚sō·sē′ā·shən]
(medicine)
Independent, uncoordinated functioning of the atria and ventricles.
(microbiology)
The appearance of a novel colony type on solid media after one or more subcultures of the microorganism in liquid media.
(physical chemistry)
Separation of a molecule into two or more fragments (atoms, ions, radicals) by collision with a second body or by the absorption of electromagnetic radiation.
(psychology)
The segregation of ideas from their affects or feelings, resulting in independent functioning of these components of a person's mental processes.
References in periodicals archive ?
The better mental marathon seems to occur in the realm of external focus: external dissociation left a good deal of its adherents unscathed by the Wall, even though dissociating internally did not (they fared among the worst).
A Dissociation Model of Borderline Personality Disorder closely analyzes one of the major issues of borderline personality disorder: dissociation and a lack of self.
BEIRUT: Patrice Paoli, France's Ambassador to Lebanon expressed to Prime Minister Najib Mikati Tuesday his country's support for the government's dissociation policy, highlighting the need to boost Francophone ties.
We suggest that one element contributing to this intractability is that the role of dissociation in mediating the disorder either is not recognized or is insufficiently accounted for in most treatment approaches.
The most influential person who devoted his life to the elaboration of the concept of dissociation was Pierre Janet.
Moreover, our results confirm, in a nonclinical sample, the link between anger and dissociation observed in psychiatric patients.
Dissociation separates the gas into its nitrogen and oxygen components without generating high temperatures, and uses the energy that comes from breaking the bond between the nitrogen and oxygen to expand the gas.
Consistent dissociation of the various elements -- building from roof, living quarters from circulation, open from enclosed areas -- gives a measure of transparency through the building linking the grassland landscape to that of the bush.
Because I know fusion and dissociation while loving the middle, Because someday I will die and not understand why, Because every year small war grows on small war, Because poetry is an expedition for the wild metaphor, Because my blood lifts into the ocean, carrying the Ages before, after me, I wonder what dream loosened from the nerve of God carries me, tooth-broken, stunned, to this shore.
post-traumatic Ellen stress syndrome), with its attendant classic symptoms--memory loss (inability to remember gay history before Ellen came out), dissociation (inability to associate with gay organizations.