CHEMISTRY GLOSSARY

Butler-Volmer equation    →   Butler-Volmerova jednadžba

Butler-Volmer equation is an activation controlled reaction, the one for which the rate of reaction is controlled solely by the rate of the electrochemical charge transfer process, which is in turn an activation-controlled process. This gives rise to kinetics that are described by the Butler-Volmer equation:

where i_o is exchange current density, η is overpotential (η = E - E_o), n is number of electrons, α_A is anodic transfer coefficient, and α_C is cathodic transfer coefficient

effervescence    →   pjenušanje

Effervescence is the formation of gas bubbles in a liquid by a chemical reaction. An example of effervescence is the release of carbon dioxide which bubbles as a gas from the liquid when limestone chips, which are composed of calcium carbonate, are added to dilute hydrochloric acid.

effusion    →   efuzija

Effusion is the flow of a gas through a small aperture. The relative rates at which gases effuse, under the same conditions, is approximately inversely proportional to the square of their densities.

Born-Haber cycle    →   Born-Haberov kružni proces

Born-Haber cycle is a cycle of reactions used for calculating the lattice energies of ionic crystalline solids. For a compound MX, the lattice energy is the enthalpy of the reaction

The standard enthalpy of formation of the ionic solid is the enthalpy of the reaction

The cycle involves equating this enthalpy (which can be measured) to the sum of the enthalpies of a number of steps proceeding from the elements to the ionic solid. The steps are:

1) Atomization of the metal

2) Atomization of the nonmetal

3) Ionisation of the metal

This is obtained from the ionisation potential.

4) Ionisation of the nonmetal

This is electron affinity.

5) Formation of the ionic solids

Equation of the enthalpies gives

from which ΔH_L can be found.

calorimeter    →   kalorimetar

Calorimeter is an instrument used to measure the energy absorbed or released in a chemical reaction. It also used in determining specific heat.

catalyst    →   katalizator

Catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Catalysts that have the same phase as the reactants are homogenous catalysts (e.g. enzymes in biochemical reactions). Those that have a different phase are heterogeneous catalyst (e.g. metals or oxides used in gas reactions).

The catalyst provides an alternative pathway by which the reaction can proceed, in which the activation energy is lower. In thus increases the rate at which the reaction comes to an equilibrium, although it does not alter the position of the equilibrium.

cathode    →   katoda

Cathode is a negative electrode of an electrolytic cell to which positively charged ions (cations) migrate when a current is passed as in electroplating baths.

In a primary or secondary cell (battery or accumulator) the cathode is the electrode that spontaneously becomes negative during discharge, and form which therefore electrons emerge.

In vacuum electronic devices electrons are emitted by the cathode and flow to the anode.

cell potential    →   potencijal članka

Cell potential (E) is difference between anode and cathode potential. If the cell potential is positive, then the reaction is spontaneous.

chemical change    →   kemijska promjena

Chemical change is a process which results in the production of one or more new materials. The system within which the process takes place is called a chemical system. A chemical change is also known as a chemical reaction, where one substance is converted into one or more different substances. When sodium and chlorine react to produce sodium chloride, a chemical reaction has taken place.

equivalent    →   ekvivalent

Equivalent (eq) is a unit for describing the amount of a chemical species. In contrast to the mole, the amount of a substance contained in one equivalent can vary from reaction to reaction.