dissociation

dissociation in chemistry, separation of a substance into atoms or ions. Thermal dissociation occurs at high temperatures. For example, hydrogen molecules (H ₂ ) 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.

dissociate XVII. f. pp. stem of L. dissociāre, f. DIS- 1 + sociāre join together, f. socius companion; see -ATE 3.
So dissociation XVII.