Dissociation in chemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into other things such as atoms, ions, or radicals, usually in a reversible manner.
For instance, when an acid dissolves in water, a covalent bond between an electronegative atom and a hydrogen atom is broken by heterolytic fission, which gives a proton (H+) and a negative ion.
In case of very strong acids and bases, degree of dissociation will be close to 1.
Less powerful acids and bases will have lesser degree of dissociation.
There is a simple relationship between this parameter and the van 't Hoff factor
The dissociation of salts by solvation in a solution, such as water, means the separation of the anions and cations.
An electrolyte refers to a substance that contains free ions and can be used as an electrically conductive medium.
Most of the solute does not dissociate in a weak electrolyte, whereas in a strong electrolyte a higher ratio of solute dissociates to form free ions.
A weak electrolyte is a substance whose solute exists in solution mostly in the form of molecules (which are said to be "undissociated"), with only a small fraction in the form of ions.
Simply because a substance does not readily dissolve does not make it a weak electrolyte.
Acetic acid is extremely soluble in water, but most of the compound dissolves into molecules, rendering it a weak electrolyte.
Again, the strength of an electrolyte is defined as the percentage of solute that is ions, rather than molecules.
Strong acids and bases are good examples, such as HCl and H2SO4.
Various relationships between Kp and α exist depending on the stoichiometry of the equation.
The example of dinitrogen tetroxide (N2O4) dissociating to nitrogen dioxide (NO2) will be taken.
If the initial concentration of dinitrogen tetroxide is 1 mole per litre, this will decrease by α at equilibrium giving, by stoichiometry, α moles of NO2.
Thus, substituting the mole fractions with actual values in term of α and simplifying;
The addition of pressure to the system will increase the value of pT, so α must decrease to keep Kp constant.
In fact, increasing the pressure of the equilibrium favours a shift to the left favouring the formation of dinitrogen tetroxide (as on this side of the equilibrium there is less pressure since pressure is proportional to number of moles) hence decreasing the extent of dissociation α.
The double arrow means that this is an equilibrium process, with dissociation and recombination occurring at the same time.
This implies that the acid dissociation constant However a more explicit description is provided by the Brønsted–Lowry acid–base theory, which specifies that the proton H+ does not exist as such in solution but is instead accepted by (bonded to) a water molecule to form the hydronium ion H3O+.
The reaction can therefore be written as and better described as an ionization or formation of ions (for the case when HA has no net charge).
is not included because in dilute solution the solvent is essentially a pure liquid with a thermodynamic activity of one.
[2]: 708 It serves as an indicator of the acid strength: stronger acids have a higher Ka value (and a lower pKa value).
Fragmentation of a molecule can take place by a process of heterolysis or homolysis.
The dissociation constant Kd is used as indicator of the affinity of the ligand to the receptor.