CHEMISTRY GLOSSARY

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

redox potential    →   redoks potencijal

Redox potential is the potential of a reversible oxidation-reduction electrode measured with respect to a reference electrode, corrected to the hydrogen electrode, in a given electrolyte.

Lennard-Jones potential    →   Lennard-Jonesov potencijal

The Lennard-Jones potential (or 12-6 potential) is a mathematically simple model that describes the interaction between two non-bonded and uncharged atoms (known as the van der Waals interaction). It was first proposed in 1924 by British physicist Sir John Edward Lennard-Jones (1894-1954). The Lennard-Jones Potential is given by the following equation

where V is the intermolecular potential between the two atoms or molecules, ε is the well depth and a measure of how strongly the two particles attract each other, σ is the distance at which the intermolecular potential between the two particles is zero, r is the distance of separation between centres of both particles.

potential energy    →   potencijalna energija

Potential energy (E_p) is the energy stored in a body or system as a consequence of its position, shape, or state (this includes gravitation energy, electrical energy, nuclear energy, and chemical energy). Gravitational potential energy is the energy associated with the state of separation between bodies that attracts each other via gravitational force. Elastic potential energy is the energy associated with the state of compression or extension of an elastic object. Thermal energy is associated with the random motions of atoms and molecules in a body.

negative pole    →   negativan pol

Negative pole is that half-cell in electrochemical cell that has the most negative electrode potential.

overpotential    →   prenapon

Overpotential (η) is a potential that must be applied in an electrolytic cell in addition to the theoretical potential required to liberate a given substance at an electrode. The value depends on the electrode material and on the current density.

positive pole    →   pozitivni pol

Positive pole is that half-cell in the electrochemical cell which has the most positive electrode potential.

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).

standard hydrogen electrode    →   standardna vodikova elektroda

Standard hydrogen electrode is a system in which hydrogen ion and gaseous hydrogen are present in their standard states. The convention is to designate the cell so that the standard hydrogen electrode is written first.

The electrode is used as a reference (of zero) for the values of other standard electrode potentials.

activation energy    →   energija aktivacije

Activation energy (E_a) is the energy that must be added to a system in order for a process to occur, even though the process may already be thermodynamically possible. In chemical kinetics, the activation energy is the height of the potential barrier separating the products and reactants. It determines the temperature dependence on the reaction rate.