CHEMISTRY GLOSSARY

indicator    →   indikator

Indicator is a substance used to show the presence of a chemical substance or ion by its colour. Acid-base indicators are compounds, such as phenolphtaleine and methyl orange, which change colour reversibly, depending on whether the solution is acidic or basic. Oxidation-reduction indicators are substances that show a reversible colour change between oxidised and reduced forms.

inert electrode    →   inertna elektroda

Inert electrode is an electrode that serves only as a source or sink for electrons without playing a chemical role in the electrode reaction. Precious metals, mercury, and carbon are typically used as inert electrodes. The inert nature of the electrode can sometimes be questioned. While the electrode may not take part in the reaction as a reactant or product, it still can act as an electrocatalyst.

ion-product constant    →   ionski produkt vode

The ion-product constant. For the reaction:

the equilibrium expression would be:

Note that all pure liquid terms are omitted, hence H₂O does not appear in the denominator. At 25 °C

law of conservation of mass    →   zakon o očuvanju mase

Law of conservation of mass states that no detectable gain or loss in mass occurs in chemical reactions. The state of a substance may change in a chemical reaction, for example, from a solid to a gas, but its total mass will not change. Note that the energy released (exothermic) or adsorbed (endothermic) in a chemical reaction is a result of energy transfer between atoms and their environment.

lithium    →   litij

Lithium was discovered by Johan August Arfvedson (Sweden) in 1817. The origin of the name comes from the Greek word lithos meaning stone, apparently because it was discovered from a mineral source whereas the other two elements, sodium and potassium, were discovered from plant sources. It is soft silvery-white metal. Lightest of metals. Reacts slowly with water and oxygen. Flammable. Can ignite in air. Reacts with water to give off a flammable gas. Lithium is obtained by passing electric charge through melted lithium chloride and from the silicate mineral called spodumene [LiAl(Si₂O₆)]. Used in batteries. Also for certain kinds of glass and ceramics. Some is used in lubricants.

termination    →   terminacija

Termination is the final step in a free radical mechanism that results in the stopping of the free radical reaction.

theoretical yield    →   teoretski prinos

Theoretical yield is the maximum quantity of a product that could be formed in a chemical reaction if all the limiting reactants reacted to form products (distinguished from actual yield).

lead-acid battery    →   olovni akumulator

Lead-acid battery is a electrical storage device that uses a reversible chemical reaction to store energy. It was invented in 1859 by French physicist Gaston Planté. Lead-acid batteries are composed of a lead(IV) oxide cathode, a sponge metallic lead anode and a sulphuric acid solution electrolyte.

In charging, the electrical energy supplied to the battery is changed to chemical energy and stored. The chemical reaction during recharge is normally written:

In discharging, the chemical energy stored in the battery is changed to electrical energy. During discharge, lead sulfate (PbSO4) is formed on both the positive and negative plates. The chemical reaction during discharge is normally written:

Lead acid batteries are low cost, robust, tolerant to abuse, tried and tested. For higher power applications with intermittent loads however, they are generally too big and heavy and they suffer from a shorter cycle life.

Nernst’s electrode potential equation    →   Nernstova jednadžba za elektrodni potencijal

For general reaction of some redox system

dependence of electrode potential of redox system upon activity of oxidised and reduced form in solution is described in Nernst’s equation for electrode potential:

where E = to electrode potential of redox system

E° = standard electrode potential of redox system

R = universal gas constant

T = thermodymical temperature

F = Faraday’s constant

z = number of electrons exchanged in redox reaction

a_O = activity of oxidised form

a_R = activity of reduced form

n = stechiometrical coefficient of oxidised form

m = stechiometrical coefficient of reduced form

theories of catalysis    →   teorije katalize

Theories of catalysis explain the influence of the catalysts upon the rate of a reaction by describing the detailed mechanism by which the catalyst is involved in the steps of the chemical reaction.