CHEMISTRY GLOSSARY

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.

activation energy    →   energija aktivacije

Activation energy (E_a) is the energy that must be added to a system in order for a process to occur, even though the process may already be thermodynamically possible. In chemical kinetics, the activation energy is the height of the potential barrier separating the products and reactants. It determines the temperature dependence on the reaction rate.

agarose    →   agaroza

Agarose is a polysaccharide obtained from agar that is used for a variety of life science applications especially in gel electrophoresis. The structure of agarose consists of alternating (1→3)-linked β-D-galactopyranose and (1→4)-linked 3,6-anhydro-α-L-galactopyranose.

allomerism    →   alomerija

Allomerism is the appearance of substances with different chemical composition but the same crystalline form.

AMU    →   AMU

AMU or atomic mass unit is a unit of mass used to express relative atomic masses. It is equal to 1/12 of the mass of an atom of the isotope carbon-12 and is equal to 1.66 033×10^-27 kg. This unit superseded both the physical and a chemical mass unit based on oxygen-16 and is sometimes called the unified mass unit or the dalton.

anion exchange    →   anionski izmjenjivač

An anionic resin has negative ions built into its structure and therefore exchanges positive ions. In an anion exchange, the side groups are ionised basic groups, such as (-NH₂, -NRH, -NR₂, -NR₃⁺) to which anions OH^- are attached. The exchange reaction is one in which different anions in the solution displace the OH^- from the solid.

anisotropy    →   anizotropija

Anisotropy is the property of molecules and materials to exhibit variations in physical properties along different molecular axes of the substance.

active site    →   aktivno mjesto

Active site is a pocket or crevice on an enzyme molecule that fits reactant molecules like a hand in a glove. The active site lowers the activation energy for reaction

activity    →   aktivitet

Activity (a) is a thermodynamic function used in place of concentration in equilibrium constants for reactions involving nonideal gases and solutions. For the species i activity is defined as

where a_i is the activity of the species i, c_i is its molar concentration, and f_i is a dimensionless quantity called the activity coefficient.

activity coefficient    →   koeficijent aktiviteta

Activity coefficient (γ or f) is a fractional number which, when multiplied by the molar concentration of a substance in solution, yields the chemical activity. This term gives an idea of how much interaction exists between molecules at higher concentration.

In solutions of very low ionic strength, when m is less than 0.01, the Debye-Hückel limiting law can be used to calculate approximate activity coefficients

where γ_i = activity coefficient of the species i, z_i = charge on the species i and μ = ionic strength of the solution.