CHEMISTRY GLOSSARY

fugacity    →   fugacitet

Fugacity (f) is a thermodynamic function used in place of partial pressure in reactions involving real gases and mixtures. For a component of a mixture, it is defined by

where μ is the chemical potential.

The fugacity of a gas is equal to the pressure if the gas is ideal. The fugacity of a liquid or solid is the fugacity of the vapour with which it is in equilibrium. The ratio of the fugacity to the fugacity in some standard state is the activity.

Gibbs free energy    →   Gibbsova slobodna energija

Gibbs free energy (G) is an important function in chemical thermodynamics, defined by

where H is the enthalpy, S the entropy, and T the thermodynamic temperature. Gibbs free energy is the energy liberated or absorbed in a reversible process at constant pressure and constant temperature. Sometimes called Gibbs energy and, in older literature, simply free energy.

Changes in Gibbs free energy, ΔG, are useful in indicating the conditions under which a chemical reaction will occur. If ΔG is negative the reaction will proceed spontaneously to equilibrium. In equilibrium position ΔG = 0.

reactant    →   reaktant

Reactants are initial materials in a chemical reaction.

reaction mechanism    →   reakcijski mehanizam

Reaction mechanism is a list of all elementary reactions that occur in the course of an overall chemical reaction.

reactivity    →   reaktivnost

Reactivity is the tendency of a compound to chemically react with other substances or itself, resulting in the release of energy.

reagent    →   reagens

Reagents are any substance used in a chemical reaction to detect, measure, examine, or produce other substances.

reversible cell    →   povrativi članak

Reversible cell is an electrical cell the chemical action in which can be reversed by passing through it a current opposite in direction to that generated by the cell.

sample    →   uzorak

In chemical analysis total amount of matter is not analysed, but only a smaller part of it. This small part is called analysis sample and it must represent the whole amount of the matter that is being analysed.

galvanic celll    →   galvanski članak

Galvanic cell (voltaic cell) is a simple device with which chemical energy is converted into electrical energy. Galvanic cells consist of two separate compartments called half cells containing electrolyte solutions and electrodes that can be connected in a circuit. Two dissimilar metals (e.g., copper and zinc) are immersed in an electrolyte. If the metals are connected by an external circuit, one metal is reduced (i.e., gains electrons) while the other metal is oxidized (i.e., loses electrons).

In the example above, copper is reduced and zinc is oxidized. The difference in the oxidation potentials of the two metals provides the electric power of the cell.

A voltaic cell can be diagrammed using some simple symbols. In the diagram the electrodes are on the outer side of the diagram and a vertical line (|) is used to separate the electrode from the electrolyte solution found in the compartment. A double vertical line (||) is used to separate the cell compartments and is symbolic of the salt bridge. Usually in a diagram the species oxidized is written to the left of the double slash. Here is an example of the Daniell cell:

The names refer to the 18th-century Italian scientists Alessandro Volta (1745-1827) and Luigi Galvani (1737-1798).

groups in periodic system of elements    →   skupine periodnog sustava

Periodic system of elements is divided into 18 groups of chemical elements. Elements belonging to the same group have a same number of valence electrons and similar chemical properties. Elements of main groups are in 1., 2., and in groups 13. to 18. Different groups of elements can be named according to the first element in the group (elements of boron group, elements of carbon group), or they have some special names (noble gases, halogenic elements, halyde elements, earthalkali and alkali metals).