CHEMISTRY GLOSSARY

non-Newtonian fluid    →   nenewtonski fluid

Non-Newtonian fluid is a fluid whose viscosity changes when the gradient in flow speed changes. Colloidal suspensions and polymer solutions like ketchup and starch/water paste are non-Newtonian fluids.

dissociation constant    →   konstanta disocijacije

Dissociation constant is a constant whose numerical value depends on the equilibrium between the undissociated and dissociated forms of a molecule. A higher value indicates greater dissociation.

The term dissociation is also applied to ionisation reactions of acids and bases in water. For example

which is often regarded as a straightforward dissociation into ions

The equilibrium constant of such a dissociation is called the acid dissociation constant or acidity constant, given by

The concentration of water [H₂O] can be taken as constant.

Similarly, for a base, the equilibrium

is also a dissociation; with the base dissociation constant or basicity constant, given by

K_a (K_b) is a measure of the strength of the acid (base).

Einstein, Albert    →   Einstein, Albert

Albert Einstein (1879-1955) is a German born American physicist, who took Swiss nationality in 1901. A year later he went to work in the Bern patent office. In 1905. he published five enormously influential papers, one on Brownian movement, one on the photoelectric effect, one on the special theory of relativity, and one on energy and inertia (which included the famous expression E = mc²). In 1915 he published the general theory of relativity, concerned mainly with gravitation. In 1921 he was awarded the Nobel Prize. In 1933, as a Jew, Einstein decided to remain in the USA (where he was lecturing), as Hitler had come to power. For the remainder of his life he sought a unified field theory. In 1939 he informed president Roosevelt that an atom bomb was feasible and that. Germany might be able to make one.

oxidating agent    →   oksidans

Oxidating agent is a substance that receives electrons and oxidates other substances. Oxidating agent is always reduced in this reaction.

oxidation    →   oksidacija

The term oxidation originally meant a reaction in which oxygen combines chemically with another substance. More generally, oxidation is a part of a chemical reaction in which a reactant loses electrons (increases oxidation number). Simultaneous reduction of a different reactant must occur (redox reaction).

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.

electrolysis    →   elektroliza

Electrolysis is the decomposition of a substance as a result of passing an electric current between two electrodes immersed in the sample.

electrolytic cell    →   elektrolitska ćelija

Electrolytic cell is an electrochemical cell that converts electrical energy into chemical energy. The chemical reactions do not occur spontaneously at the electrodes when they are connected through an external circuit. The reaction must be forced by applying an external electric current. It is used to store electrical energy in chemical form (rechargeable battery). It is also used to decompose or produce (synthesise) new chemicals by the application of electrical power. This process is called electrolysis, e.g., water can be decomposed into hydrogen gas and oxygen gas. The free energy change of the overall cell reaction is positive.

polycondensational polymer    →   polikondenzacijski polimer

Polycondensational polymers are compounds which are obtained by condensation polymerization with successive repetitions of the condensation reaction.

precipitate    →   precipitat

Precipitate or the deposit is an insoluble solid formed by reactions in a solution. For example, when a solution of silver nitrate is added to a solution of sodium chloride, insoluble silver chloride precipitates.