CHEMISTRY GLOSSARY

electric cell    →   električni članak

Electric cell (battery) is a device that is capable of changing some form of energy, such as chemical, nuclear or radiant energy, into electricity. A solar cell, for example, consists of a semiconductor junction that converts sunlight directly into electricity. A dry cell battery converts chemical energy into electricity.

heterogenic reaction    →   heterogena reakcija

Heterogenic reactions are those reactions which take place in different phases (in different aggregate states).

Heusler alloys    →   Heusler legure

Heusler alloys are alloys of manganese, copper, aluminium, nickel, and sometimes other metals which find important uses as permanent magnets.

hologram    →   hologram

Hologram is reconstruction of an object in three dimensions by using the properties of laser light (interference). A hologram takes a picture, but displays it so the side and the rear can be seen.

electric field    →   električno polje

If a small amount of charge experience a force, there is an electric field in the vicinity. Electric field E is defined in terms of electrostatic force F that would be exerted on positive test charge q_p placed in the field:

SI unit for electric field is N C^-1, or V m^-1.

The electric field due to a point charge q at distance r from it given by:

where ε₀ is permittivity constant, and is ε_o=8.85×10^-12 C² N^-1 m^-2.

electrical double layer    →   električni dvosloj

Electrical double layer is the structure of charge accumulation and charge separation that always occurs at the interface when an electrode is immersed into an electrolyte solution. The excess charge on the electrode surface is compensated by an accumulation of excess ions of the opposite charge in the solution. The amount of charge is a function of the electrode potential. This structure behaves essentially as a capacitor. There are several theoretical models that describe the structure of the double layer. The three most commonly used ones are the Helmholtz model, the Gouy-Chapman model, and the Gouy-Chapman-Stern model.

electrochemical cell    →   elektrokemijski članak

Electrochemical cell is a device that converts chemical energy into electrical energy or vice versa when a chemical reaction is occurring in the cell. It consist of two electronically conducting phases (e.g., solid or liquid metals, semiconductors, etc) connected by an ionically conducting phase (e.g. aqueous or non-aqueous solution, molten salt, ionically conducting solid). As an electric current passes, it must change from electronic current to ionic current and back to electronic current. These changes of conduction mode are always accompanied by oxidation/reduction reactions.

An essential feature of the electrochemical cell is that the simultaneously occurring oxidation-reduction reactions are spatially separated. E.g., in a spontaneous chemical reaction during the oxidation of hydrogen by oxygen to water, electrons are passed directly from the hydrogen to the oxygen.

In contrast, in the spontaneous electrochemical reaction in a galvanic cell the hydrogen is oxidised at the anode by transferring electrons to the anode and the oxygen is reduced at the cathode by accepting electrons from the cathode. The ions produced in the electrode reactions, in this case positive hydrogen ions and the negative hydroxyl (OH^-) ions, will recombine in the solution to form the final product of the reaction: water. During this process the electrons are conducted from the anode to the cathode through an outside electric circuit where the electric current can drive a motor, light a light bulb, etc. The reaction can also be reversed: water can be decomposed into hydrogen and oxygen by the application of electrical power in an electrolytic cell.

holography    →   holografija

Holography is a technique for creating a three-dimensional image of an object by recording the interference pattern between a light beam diffracted from the object and a reference beam. The image can be reconstructed from this pattern by a suitable optical system.

electrochemical series    →   elektrokemijski niz

Electrochemical series is a series of chemical elements arranged in order of their standard electrode potentials. The hydrogen electrode

is taken as having zero electrode potential. An electrode potential is, by definition, a reduction potential.

Elements that have a greater tendency than hydrogen to lose electrons to their solution are taken as electropositive; those that gain electrons from their solution are below hydrogen in the series and are called electronegative.

The series shows the order in which metals replace one another from their salts; electropositive metals will replace hydrogen from acids.

electrode of the first kind    →   elektroda prvog reda

Electrode of the first kind is a simple metal electrode immersed in a solution containing its own ion (e.g., silver immersed in a silver nitrate solution). The equilibrium potential of this electrode is a function of the concentration (more correctly of activity) of the cation of the electrode metal in the solution (see Nernst’s electrode potential equation).