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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.



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.


Independent, uncoordinated functioning of the atria and ventricles.
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.
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 ?
This alteration allowed the neck of the stem as it rotated to impinge on the locking ring at its split causing the ring to open and displace within its slot, which permitted head disassociation (Fig.
We are also very focused on insulating Lebanon from any aftermath of any response to Syria's chemical attack, and preserving Lebanon's policy of disassociation from the Syria conflict.
BEIRUT: Prime Minister Tammam Salam Tuesday said his government would continue trying to convince Hezbollah to adhere to the country's disassociation policy, at a news conference concluding his Saudi Arabia visit.
KARACHI, December 19, 2009 (Balochistan Times ): CNG Station Owners Association (CSOAP) and CNG Dealers Association (CDA) have announced disassociation from the strike call given by a CNG association for December 20, 2009.
Public opinion, the admissions process, unexamined assumptions, the slow demise of a liberal education, six challenges to universities including the glut of information and commercialization, the rising dominance of marketing over educational goals, "dumbing down," student disassociation, the new elitism, and the idea that a higher education is only a way station on the road to getting a job.
Mental association and disassociation techniques help users increase performance and minimize the discomfort of high levels of exertion.
Rejecting the Lebanese government's self-declared disassociation policy on the conflict as an act of "cowardice," he admitted his party's involvement in the Syrian fighting, saying: "We are part of Syria's battle.
The EU strongly calls on all parties, including Hezbollah, to act responsibly, fully abide by Lebanon's disassociation policy from the conflict in Syria and support the efforts of President [Michel] Sleiman to implement the provisions of the Bbda Declaration.
Gene Pian, President and CEO of SETO, commented that we were more than satisfied with the results of the current quarter since it had experienced an absorption of one time expenses associated with the aforementioned disassociation of (Fimas) and the discontinuation of (Fuji).
NNA - Former Prime Minister, Fouad Siniora, called for an active implementation of the disassociation policy towards the Syrian crisis, through a thorough commitment to Bbda Declaration.
GILGIT, April 19, 2010 (Balochistan Times): Secretary General JUI-F and member of Gilgit-Baltistan Council (upper house) Maulana Attaullah Shahab has said a new political era has dawned in Gilgit-Baltistan but it faces four major challenges which will have to be addressed to protect the system Maulana Attaullah Shahab said these lunar eclipses are sectarianism, showing disassociation from Kashmir, lack of constitutional protection to the present system and expectations of the masses from Mehdi Government in the context of education, health, job opportunities and law and order.
He identifies a kind of madness that resulted and was perpetuated in individuals and families--a condition that produced sad cases of disassociation and debilitation in some, and in others, intense creativity.