CHEMISTRY GLOSSARY

racemisation    →   racemizacija

Racemisation is a conversion, by heat or by chemical reaction, of an optically active compound into an optically inactive form which half of the optically active substance becomes its miror image (enantiomer).

equilibrium constant    →   konstanta ravnoteže

The equilibrium constant (K) was originally introduced in 1863 by Norwegian chemists C.M. Guldberg and P. Waage using the law of mass action. For a reversible chemical reaction represented by the equation

chemical equilibrium occurs when the rate of the forward reaction equals the rate of the back reaction, so that the concentrations of products and reactants reach steady-state values.

The equilibrium constant is the ratio of chemical activities of the species A, B, C, and D at equilibrium.

To a certain approximation, the activities can be replaced by concentrations.

For gas reactions, partial pressures are used rather than concentrations

The units of K_p and K_c depend on the numbers of molecules appearing in the stoichiometric equation (a, b, c, and d).

The value equilibrium constant depends on the temperature. If the forward reaction is exothermic, the equilibrium constant decreases as the temperature rises. The equilibrium constant shows the position of equilibrium. A low value of K indicates that [C] and [D] are small compared to [A] and [B]; i.e. that the back reaction predominates.

The equilibrium constant is related to Δ_rG°, the standard Gibbs free energy change in the reaction, by

radical    →   radikal

Radical is a reaction intermediate where a bond is broken and the two parts of the molecule exist carrying a single unshared electron. The radicals are normally destroyed quickly by recombination or they break into another radical and a stable molecule.

rate equation    →   jednadžba brzine reakcije

Rate equation is an equation that describes the dependence of reaction rate on concentrations of reacting species. It always has the form

where a and b are usually integral exponents.

reactant    →   reaktant

Reactants are initial materials in a chemical reaction.

explosive    →   eksploziv

Explosive is a compound or mixture that, when ignited or detonated, undergoes rapid violent chemical reaction that produces large amount of gas and heat, accompanied by light, sound and a high pressure shock wave.

Faraday’s laws of electrolysis    →   Faradayevi zakoni elektrolize

Faraday’s laws of electrolysis are two laws found by British chemist and physicist Michael Faraday (1791-1867) in his experiments on electrolysis:

1. The quantity of matter extracted on the electrode is proportional to the quantity of charge (Q = I·t) which has flown in electrolysis time.

where z = number of electrons changed in reaction and F = Faraday’s constant which equals 96 487 C mol^-1.

2. The masses of the elements liberated by the same quantity of electricity are directly proportional to their chemical equivalents.

96 487 C will discharge 1 mol Ag and 1/2 mol Cu. The relevant half reactions are:

fission    →   fisija

Fission is a nuclear reaction in which an atomic nucleus breaks into smaller nuclei of comparable mass, releasing a large amount of energy.

reactivity series    →   reaktivni niz

Reactivity series or activity series is a series of elements (usually metals) ranked by their reactivity degree, made for comparison of reactions of elements with other substances, e.g. acids and oxygen.

reagent    →   reagens

Reagents are any substance used in a chemical reaction to detect, measure, examine, or produce other substances.