CHEMISTRY GLOSSARY

Boltzmann constant    →   Boltzmannova konstanta

The Boltzmann constant (k or k_B) is the physical constant describing the relationship between the thermodynamic temperature and the average kinetic energy of particles in a gas. It equals the molar gas constant R divided by the Avogadro constant N_A and has the value 1.380 648 52(79)×10^-23 J/K. It is named after the Austrian physicist Ludwig Eduard Boltzmann (1844-1906).

harmonic motion    →   harmoničko gibanje

Harmonic motion is caused by restoring force, acting on a body that is displaced from its equilibrium position. This force tries to put the body back in equilibrium. Usual examples are the motion of a body attached to elastic spring (see: Hooke’s law) and the motion of mathematical pendulum. The body undergoes periodic motion around the equilibrium point.

Helmholz free energy    →   Helmholzova slobodna energija

Helmholz free energy (A) is a thermodynamic function defined by A = U - TS, where U is the internal energy, S the entropy, and T the thermodynamic temperature. For a reversible isothermal process ΔA represents the useful work available.

isothermal process    →   izotermni proces

Isothermal process is a thermodynamic process in which the temperature of the system does not change.

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.

Celsius temperature scale    →   Celsiusova temperaturna skala

For value of zero in Celsius temperature scale the freezing point of water at a pressure of 101 325 Pa is taken. The boiling point of water at a pressure of 101 325 Pa is taken as another reference point. This range is divided into 100 equal parts, and each part is an equivalent to 1 °C. Units of Celsius temperature scale (°C) and thermodynamic temperature scale (K) are identical

1 °C = 1 K.

Rankine cycle    →   Rankineov ciklus

Rankine cycle is a thermodynamic cycle which can be used to calculate the ideal performance of a heat engine that uses a condensable vapour as the working fluid.

thermodynamic equilibrium    →   termodinmička ravnoteža

Thermodynamic equilibrium is a system equilibrium in which energy that it gains from its surroundings is exactly balanced by the energy that it loses, no matter how much time is allowed to pass.

Curie    →   Curie

Maria Sklodowska-Curie (1867-1934) Polish-born French chemist who went to Paris in 1891. She married the physicist Pierre Curie (1859-1906) in 1985 and soon began work on seeking radioactive elements other than uranium in pitchblende (to account for its unexpectedly high radioactivity). By 1898 she had discovered radium and polonium although it took her years to purify them. In 1903 the Curies shared the Nobel Prize for physics with Henri Becquerel, who had discovered radioactivity.

diffusion    →   difuzija

Diffusion is the spontaneous mixing of one substance with another when in contact or separated by a permeable membrane. Diffusion is a result of the random motions of their component atoms, molecules, ions, or other particles. Diffusion occurs most readily in gases, less so in liquids, and least in solids. The rate of diffusion is proportional to the concentration of the substance and increases with temperature. The theoretical principles are stated in Fick’s laws.