CHEMISTRY GLOSSARY

p-value    →   p-vrijednost

Concentration of dissolved component shown as a negative logarithm is called p-value.

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.

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

reaction order    →   red reakcije

Order of a reaction (n) is the sum of the exponents of the concentration terms in a rate equation.

Total order of a reaction is

smog    →   smog

Smog is a mixture of smoke and fog. The term is used to describe city fogs in which there is a large proportion of particulate matter (tiny pieces of carbon from exhausts) and also a high concentration of sulphur and nitrogen gases.

soft water    →   meka voda

Soft water is any water that does not contain large concentrations of the dissolved minerals calcium or magnesium.

gallium    →   galij

Gallium was discovered by Lecoq de Boisbaudran (France) in 1875. The origin of the name comes from the Latin word Gallia meaning France. It is soft, blue-white metal. Stable in air and water. Reacts violently with chlorine and bromine. Gallium is found throughout the crust in minerals like bauxite, germanite and coal. Used in semiconductor production. It us used in making LED’s (light-emitting diodes) and GaAs laser diodes.

germanium    →   germanij

Germanium was discovered by Clemens Winkler (Germany) in 1886. The origin of the name comes from the Latin word Germania meaning Germany. It is greyish-white semi-metal. Unaffected by alkalis and most (except nitric) acids. Stable in air and water. Germanium is obtained from refining copper, zinc and lead. Widely used in semiconductors. It is a good semiconductor when combined with tiny amounts of phosphorus, arsenic, gallium and antimony.

glass electrode    →   staklena elektroda

Glass electrode is a hydrogen-ion responsive electrode usually consisting of a bulb, or other suitable form, of special glass attached to a stem of high resistance glass complete with internal reference electrode and internal filling solution system. Glass electrode is also available for the measurement of sodium ions.

The glass electrode, which consists of a thin wall glass bulb, has an extremely high electrical resistance. The membrane of a typical glass electrode (with a thickness of 0.03 mm to 0.1 mm) has an electrical resistance of 30 MΩ to 600 MΩ. The surface of a glass membrane must be hydrated before it will function as a pH electrode. When a glass surface is immersed in an aqueous solution then a thin solvated layer (gel layer) is formed on the glass surface in which the glass structure is softer. This applies to both the outside and inside of the glass membrane.

The simplest explanation for the working of the thin glass electrode is that the glass acts as a weak acid (Glass-H).

The hydrogen ion activity of the internal solution is held constant. When a solution of different pH from the inside comes in contact with the outside of the glass membrane, the glass is either deprotonated or protonated relative to the inside of the glass. The difference in pH between solutions inside and outside the thin glass membrane creates electromotive force in proportion to this difference in pH.

spectrophotometry    →   spektrofotometrija

Spectrophotometry is a determination of the concentration of a material in a sample by measurement of the amount of light the sample absorbs.