CHEMISTRY GLOSSARY

ion-product constant    →   ionski produkt vode

The ion-product constant. For the reaction:

the equilibrium expression would be:

Note that all pure liquid terms are omitted, hence H₂O does not appear in the denominator. At 25 °C

magnetic permeability    →   magnetska permeabilnost

Magnetic permeability (μ), also called permeability, is a constant of proportionality that exists between magnetic induction and magnetic field intensity. This constant is equal to approximately μ_o = 1.257×10^-6 H/m in a vacuum.

Magnetic permeability is often expressed in relative, rather than in absolute, terms. If μ represents the permeability of the substance in question, then the relative permeability, μ_r, is given by:

mole    →   mol

Mole (mol) is the SI base unit of amount of substance.

The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kg of carbon 12.

When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. In this definition, it is understood that the carbon 12 atoms are unbound, at rest and in their ground state.

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

Newton’s gravitational law    →   Newtonov zakon gravitacije

Every object in the universe attracts every other object with a force (gravitational force F_G) directed along the line through centres of the two objects that is proportional to the product of their masses and inversely proportional to the square of the distance between them.

m₁ and m₂ are masses of the two objects and r is the distance between them. G is universal constant of gravitation, which equals 6.67•10^-26 N m² kg^-2. Strictly speaking, this law applies only to objects that can be considered pointlike object. Otherwise, the force has to be found by integrating the forces between various mass elements.

It is more properly to express Newton’s gravitational law by vector equation:

in which r₁ and r₂ are position vectors of masses m₁ and m₂.

Gravitational forces act on distance. Newton’s gravitational law is derived from Kepler’s law for planetary motion, using a physical assumption considering Sun as the centre and the source of gravitational force.

Additionally, every object moves in the direction of the force acting on it, with acceleration that is inversely proportional to the mass of object. For bodies on the surface of Earth, the distance r in gravitational law formula is practically equal to the Earth radius, R_E. If the mass of the body on Earth surface is m and the mass of earth is M_E, the gravitational force acting on that body can be expressed as:

where g is gravitational acceleration which is, although dependent on geographical latitude, usually considered as constant equal to 9.81 m s^-2.

osmotic pressure    →   osmotski tlak

Osmotic pressure (Π) is the excess pressure necessary to maintain osmotic equilibrium between a solution and a pure solvent separated by a membrane permeable only to the solvent. In an ideal dilute solution

where c_B is the amount-of-substance concentration of the solute, R is the molar gas constant, and T the temperature.

Ostwald’s dilution law    →   Ostwaldov zakon razrjeđenja

Ostwald’s dilution law is a relation for the concentration dependence of the molar conductivity Λ of an electrolyte solution, viz.

where c is the solute concentration, K_c is the equilibrium constant for dissociation of the solute, and L₀ is the conductivity at cΛ = 0. The law was first put forward by the German chemist Wilhelm Ostwald (1853-1932).

resistivity    →   električna otpornost

Electrical resistivity, or specific resistance (ρ) is the electric field strength divided by the current density when there is no electromotive force in the conductor. Resistivity is an intrinsic property of a material. Materials with low resistivity are good conductors of electricity and materials with high resistivity are good insulators.

For a conductor of uniform cross section with area A and length L, and whose resistance is R, the resistivity is given by

The SI unit is Ω m.

Schrodinger equation    →   Schrodingerova jednadžba

Schrödinger equation is the basic equation of wave mechanics which, for systems not dependent on time, takes the form:

where Ψ is the wavefunction, V is the potential energy expressed as a function of the spatial coordinates, E its total energy, ² is the Laplacian operator, h is Planck’s constant, and m is the mass.

salinity    →   salinitet

Salinity (S) is a measure of the quantity of dissolved salts in seawater. It is formally defined as the total amount of dissolved solids in seawater in parts per thousand (‰) by weight when all the carbonate has been converted to oxide, the bromide and iodide to chloride, and all organic matter is completely oxidized.

Chlorinity is the oldest of the salinity measures considered and is still a corner-stone in the study of dissolved material in seawater. Based on the principle of constant relative proportions it provides a measure of the total amount of dissolved material in seawater in terms of the concentration of halides. The relationship between chlorinity (Cl) and salinity as set forth in Knudsen’s tables is

In 1962, however, a better expression for the relationship between total dissolved salts and chlorinity was found to be

Practical Salinity (S_P) was introduced as a replacement for Chlorinity. Practical Salinity is is relatively easy to measure using standard conductometers, measurements are more precise and less time consuming than measurements of Chlorinity and accurate measurements can even be made in situ. Practical salinity S_P is defined on the Practical Salinity Scale of 1978 (PSS-78) in terms of the conductivity ratio K₁₅ which is the electrical conductivity of the sample at temperature t₆₈ = 15 °C and pressure equal to one standard atmosphere, divided by the conductivity of a standard potassium chloride (KCl) solution at the same temperature and pressure. The mass fraction of KCl in the standard solution is 0.0324356 (32.4356 g of KCl in 1 kg of solution).

Note that Practical Salinity is a unit-less quantity. Though sometimes convenient, it is technically incorrect to quote Practical Salinity in "psu". For most purposes one can assume that the psu and the ‰, are synonymous.

The global average salinity of ocean waters is about 35 ‰, that is, about 35 g of solid substances are dissolved in 1 kg of seawater.