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

normal conditions    →   normalni uvjeti

Gas is under normal (or standard) conditions when: p₀ = 10⁵ Pa and T₀ = 273.15 K (0 °C). IUPAC recommends that the former use of the pressure of 1 atm as standard pressure (equivalent to 101 325 Pa) should be discontinued. At these conditions, the molar volume of gas V_m0 is 0.022 711 m³ (22.711 L).

Nusselt number    →   Nusseltova značajka

Nusselt number (Nu) is a dimensionless quantity used in fluid mechan-ics, defined by

where h is coefficient of heat transfer, l is length, and k is thermal conductivity.

Onsager relations    →   Onsagerove relacije

Onsager relations are an important set of equations in the thermodynamics of irreversible processes. They express the symmetry between the transport coefficients describing reciprocal processes in systems with a linear dependence of flux (J_i) on driving forces (X_j).

In Onsager’s theory the coupling coefficients are equal, L_ij = L_ji. This is known as reciprocal relations. The theory was developed by the Norwegian chemist Lars Onsager (1903-1976) in 1931.

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).

Rayleigh number    →   Rayleighova značajka

Rayleigh number (Ra) is a dimensionless quantity used in fluid mechanics, defined by

where l is length, g is acceleration of gravity, α is cubic expansion coefficient, T is temperature, ρ is density, η is viscosity, and a is thermal diffusivity.

Schmidt number    →   Schmidtova značajka

Schmidt number (Sc) is a dimensionless quantity used in fluid mechanics, defined by

where η is viscosity, ρ is density, and D is diffusion coefficient.

solution composition    →   sastav otopine

Solutions are homogenous mixtures of several components. The component which is found in a greater quantity is called the solvent and the other components are called solutes. Quantitative composition of a solution can be expressed by concentration (amount, mass, volume and number), by fraction (amount, mass, and volume), ratio (amount, mass, and volume) and by molality. Amount, mass, and volume ratio are numerical, nondimensional units and are frequently expressed as percentage (% = 1/100), promile (‰ = 1/1000) or parts per million (ppm = 1/1 000 000). If it is not defined, it is always related to the mass ratio.

teflon    →   teflon

Teflon is a DuPont Company trademark for polytetrafluoroethylene (PTFE). It was discovered in 1938 by R. J. Plunkett. Teflon has the lowest coefficient of friction of any solid material known to man. It is also used as a non-stick coating for pans and other cookware. Teflon is very unreactive, and so is often used in containers and pipework for reactive chemicals. Its melting point is 327 °C.