[dih-soh-see-ey-shuhn, -shee-ey-]
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.

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.

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Dissociation is a state of acute mental decompensation in which certain thoughts, emotions, sensations, and/or memories are compartmentalized, diagnosed mostly in individuals with a history of trauma. Dissociative disorders are commonly precipitated by overwhelming stress. This stress may be provoked by seeing or experiencing an accident, a disaster or a traumatic event, including sexual abuse, and especially during childhood.


The French psychiatrist Pierre Janet (1859-1947) initially coined the term "splitting" in his book L'Automatisme psychologique. There, he emphasized its role as a defensive mechanism employed in response to psychological trauma. While he considered dissociation an initially effective defense mechanism that protects the individual psychologically from the impact of overwhelming traumatic events, a habitual tendency to dissociate would likely be a marker of a more pronounced psychopathology.

Carl Jung described pathological manifestations of dissociation as special or extreme cases of the normal operation of the psyche. This structural dissociation, opposing tension, and hierarchy of basic attitudes and functions in normal individual consciousness is the basis of Jung's Psychological Types. He theorized that dissociation is a natural necessity for consciousness to operate in one faculty unhampered by the demands of its opposite.

Attention to dissociation as a clinical feature has been growing in recent years as knowledge of post-traumatic stress disorder increased, due to interest in dissociative identity disorder and the multiple personality controversy, and as neuroimaging research and population studies show its relevance.


The DSM-IV considers symptoms such as depersonalization, derealization and psychogenic amnesia to be core features of dissociative disorders. However, in the normal population dissociative experiences that are not clinically significant are highly prevalent, with 60% to 65% of the respondents indicating that they have had some dissociative experiences. The SCID-D is a structured interview used to assess and diagnosis dissociation.

Relation to trauma and abuse

Dissociation has been described as one of a constellation of symptoms experienced by some victims of multiple forms of childhood trauma, including physical abuse and child sexual abuse. This is supported by studies which suggest that dissociation is correlated with a history of trauma. Dissociation appears to have a high specificity and low sensitivity to having a self-reported history of trauma.

Symptoms of dissociation resulting from trauma may include depersonalization, psychic numbing, disengagement, or amnesia regarding the events of the abuse. It has been hypothesized that dissociation may provide a temporarily effective defense mechanism in cases of severe trauma; however, in the long term, dissociation is associated with decreased psychological functioning and adjustment. Other symptoms sometimes found along with dissociation in victims of traumatic abuse (often referred to as "sequelae to abuse") include anxiety, PTSD, low self-esteem, somatization, depression, chronic pain, interpersonal dysfunction, substance abuse, self-multilation and suicidal ideation or actions. These symptoms may lead the victim to erroneously present the symptoms as the source of the problem.

Chu et al. (1999) reported that child abuse, especially chronic abuse starting at early ages, was related to high levels of dissociative symptoms in a clinical sample, including amnesia for abuse memories. Briere & Runtz (1988) found increased levels of dissociation in a non-clinical sample of adult women who had been sexually abused by a significantly older person prior to age 15. Another non-clinical study by the same authors found that a history of childhood sexual abuse and especially a history of childhood physical abuse were predictive of dissociative symptoms, though they stated that the validity of the scale used to measure these symptoms was yet to be proven.

The level of dissociation has been found to be related to reported overwhelming sexual and physical abuse. When severe sexual abuse (penetration, several perpetrators, lasting more than one year) had occurred, dissociative symptoms were even more prominent. The amount of dissociation that follows directly after a trauma predicts posttraumatic stress disorder (PTSD). Individuals that are more likely to dissociate during a traumatic event are considerably more likely to develop chronic PTSD. One study found that subjects who experienced early and/or recent trauma were more dissociative

In a review of clinical literature, Merckelbach and Muris (2001) argue that a causal link between trauma and dissociation has not been established and may not be true, due what they describe as "at best, modest" correlations in the literature, possibly obscured results due to uncontrolled confounding variables, and possible positive bias towards self-reports of trauma resulting due to symptoms of dissociation. Fantasy proneness, which is itself linked to self-reported abuse, is at least as predictive of measured dissociation as self-reported trauma. Merckelbach et al. (2004) questions the accuracy of self-reports of trauma by fantasy prone individuals, pointing to studies that found fantasy proneness to be related to overendorsement of implausible answers in surveys.

Psychoactive substances

Psychoactive substances can often induce a state of temporary dissociation. Substances with dissociative properties include ketamine, nitrous oxide, tiletamine, DXM, cannabis, PCP, 2C-B, salvia and ibogaine.

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