CHEMISTRY GLOSSARY

acid dissociation constant    →   konstanta disocijacije kiseline

Acid dissociation constant (K_a) is the equilibrium constant for the dissociation of an acid HA through the reaction

The quantity pK_a = -log K_a is often used to express the acid dissociation constant.

acid rain    →   kisela kiša

Acid rain is rainwater that shows acid reaction because of nitrogen and sulphur oxides absorption. It is generated mainly by industrial pollutions.

activated complex    →   aktivirani kompleks

Activated complex is an intermediate structure formed in the conversion of reactants to products. The activated complex is the structure at the maximum energy point along the reaction path; the activation energy is the difference between the energies of the activated complex and the reactants.

anode    →   anoda

Anode is the electrode at which oxidation occurs in a cell. Anions migrate to the anode.

Anode is a positive electrode on which reaction of oxidation is developed (loss of electrons).

antiparticle    →   antičestica

Antiparticle is a particle having the same mass as a given elementary particle and a charge equal in magnitude but opposite in sign.

aqueous solution    →   vodena otopina

Aqueous solutions are those solutions where water is the solvent. An aqueous solution found in an equation describing a chemical reaction is denoted by the state symbol, (aq).

acid    →   kiselina

Acid is a type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction for an acid HA is commonly written:

In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is:

This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and produce colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water, (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. acetic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant.

In the Lowry-Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). An important feature of the Lowry-Brønsted concept is that when an acid gives up a proton, a conjugate base is formed that is capable of accepting a proton.

Similarly, every base produces its conjugate acid as a result of accepting a proton.

For example, acetate ion is the conjugate base of acetic acid, and ammonium ion is the conjugate acid of ammonia.

As the acid of a conjugate acid/base pair becomes weaker, its conjugate base becomes stronger and vice versa.

A further extension of the idea of acids and bases was made in the Lewis theory. In this, a G. N. Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses "traditional" acid-base reactions, but it also includes reactions that do not involve ions, e.g.

in which NH₃ is the base (donor) and BCl₃ the acid (acceptor).

azo compounds    →   azo-spojevi

Azo compounds are organic compounds containing the group -N=N- linking two other groups. They can be formed by reaction of a diazonium ion with a benzene ring.

Boudouard’s equilibrium    →   Boudouardova ravnoteža

Boudouard’s equilibrium is established when carbon dioxide reacts with carbon. Because of reactions endothermity the temperature increase shifts the reaction rightwards and the temperature reduction leftwards.

Bronsted acid    →   Bronstedova kiselina

Brøsted acid is a material that gives up hydrogen ions in a chemical reaction.