CHEMISTRY GLOSSARY

pascal    →   paskal

Pascal (Pa) is the SI derived unit of pressure. One pascal is the pressure generated by a force of one newton acting on an area of one square metre (Pa = N/m²). It was named after the French mathematician, physicist and philosopher Blaise Pascal (1623-1662).

energy    →   energija

Energy (E, U) is the characteristic of a system that enables it to do work. Like work itself, it is measured in joules (J).

The internal energy of a body is the sum of the potential energy and the kinetic energy of its component atoms and molecules.

Potential energy 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).

Kinetic energy is the energy of motion and is usually defined as the work that will be done by a body possessing the energy when it is brought to rest. For a body of mass m having a speed v, the kinetic energy is mv²/2. Kinetic energy is most clearly exhibited in gases, in which molecules have much greater freedom of motion than in liquids and solids.

In an isolated system energy can be transferred from one form to another but the total energy of the system remains constant.

face-centered cubic lattice    →   plošno centrirana kubična rešetka

Face-centered cubic lattice (fcc or cubic-F), like all lattices, has lattice points at the eight corners of the unit cell plus additional points at the centers of each face of the unit cell. It has unit cell vectors a =b =c and interaxial angles α=β=γ=90°.

The simplest crystal structures are those in which there is only a single atom at each lattice point. In the fcc structures the spheres fill 74 % of the volume. The number of atoms in a unit cell is four (8×1/8 + 6×1/2 = 4). There are 26 metals that have the fcc lattice.

face-centered orthorhombic lattice    →   plošno centrirana ortorompska rešetka

Face-centered orthorhombic lattice (orthorhombic-F), like all lattices, has lattice points at the eight corners of the unit cell plus additional points at the centers of each face of the unit cell. It has unit cell vectors a≠b≠c and interaxial angles α=β=γ=90°.

pressure    →   tlak

Pressure (p) is the force acting normally on unit area of a surface. It is measured in pascals in Si units (Pa)

radiant power    →   snaga radijacije

Radiant power is energy of radiation striking a unit area per unit time. The SI unit of radiant power is J m^-2 s^-1.

rem    →   rem

Rem (rem) (roentgen equivalent man) is a non-SI unit of dose equivalent employed in radioprotection (rem = 10^-2 Sv).

equilibrium constant    →   konstanta ravnoteže

The equilibrium constant (K) was originally introduced in 1863 by Norwegian chemists C.M. Guldberg and P. Waage using the law of mass action. For a reversible chemical reaction represented by the equation

chemical equilibrium occurs when the rate of the forward reaction equals the rate of the back reaction, so that the concentrations of products and reactants reach steady-state values.

The equilibrium constant is the ratio of chemical activities of the species A, B, C, and D at equilibrium.

To a certain approximation, the activities can be replaced by concentrations.

For gas reactions, partial pressures are used rather than concentrations

The units of K_p and K_c depend on the numbers of molecules appearing in the stoichiometric equation (a, b, c, and d).

The value equilibrium constant depends on the temperature. If the forward reaction is exothermic, the equilibrium constant decreases as the temperature rises. The equilibrium constant shows the position of equilibrium. A low value of K indicates that [C] and [D] are small compared to [A] and [B]; i.e. that the back reaction predominates.

The equilibrium constant is related to Δ_rG°, the standard Gibbs free energy change in the reaction, by

siemens    →   simens

Siemens (S) is the SI derived unit of of electrical conductance of a conductor in which a current of one ampere is produced by an electrical potential difference of one volt (S = A·V^-1 = Ω^-1). The unit was named after the German scientist Ernst Werner von Siemens (1816-1892).

sievert    →   sivert

Sievert (Sv) is the SI derived unit of dose equivalent when the absorbed dose of ionising radiation multiplied by the stipulated dimensionless factors is 1 J/kg. It was named after the Swedish physicst Rolf Sievert (1896-1966).