CHEMISTRY GLOSSARY

heat transfer    →   prijenos topline

From observations and experiments it has been found that heat energy can be transferred from one position to another through three different modes: conduction, convection and radiation.

chemical potential    →   kemijski potencijal

For a mixture of substances, the chemical potential of constituent B (μ_B) is defined as the partial derivative of the Gibbs energy G with respect to the amount (number of moles) of B, with temperature, pressure, and amounts of all other constituents held constant.

Also called partial molar Gibbs energy. Components are in equilibrium if their chemical potentials are equal.

chlorophyll    →   klorofil

Chlorophyll is a green pigment present in green plants and cyanobacteria. Chlorophyll is essential in the transformation of light energy to chemical energy in photosynthesis. Chlorophyll absorbs light mostly in the blue and red ends of the visible spectrum, and very little in the green wavelengths. That green light is reflected, giving us the leaf colour we see.

collision theory    →   teorija sudara

Collision theory is theory that explains how chemical reactions take place and why rates of reaction alter. For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called successful collisions. The successful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants and raising the temperature bring about more collisions and therefore more successful collisions, increasing the rate of reaction.

density    →   gustoća

In the most common usage, density (ρ) is mass density or mass per unit volume. In Si units it is measured in kg m^-3. More commonly, densities are given in kg dm^-3.

More generally, it is the amount of some quantity (mass, charge, energy, etc.) divided by a length, area, or volume.

Relative density is the ratio of the density of a substance to the density of some reference substance. For liquids or solids, it is the ratio of the density (usually at 20 °C) to the density of water at 4 °C. This quantity was formerly called specific gravity.

irreversible process    →   ireverzibilni proces

If a system is taken from one state to another but cannot be brought back to the same initial state, then the process is called irreversible. Some examples are free expansion of a gas; dissipation of energy due to friction, or the mixing of two gases or liquids etc.

joule    →   džul

Joule (J) is the SI derived unit of energy, work, and heat. The joule is the work done when the point of application of a force of one newton is displaced a distance of one metre in the direction of the force (J = N m). The unit was named after the British scientist James Prescott Joule (1818-1889).

dissociation constant    →   konstanta disocijacije

Dissociation constant is a constant whose numerical value depends on the equilibrium between the undissociated and dissociated forms of a molecule. A higher value indicates greater dissociation.

The term dissociation is also applied to ionisation reactions of acids and bases in water. For example

which is often regarded as a straightforward dissociation into ions

The equilibrium constant of such a dissociation is called the acid dissociation constant or acidity constant, given by

The concentration of water [H₂O] can be taken as constant.

Similarly, for a base, the equilibrium

is also a dissociation; with the base dissociation constant or basicity constant, given by

K_a (K_b) is a measure of the strength of the acid (base).

metabolism    →   metabolizam

Metabolism is a sum of all chemical and physiological processes by which the body builds and maintains itself. It is a process of building the body’s molecular structures from nutrients (anabolism) and breaking them down for energy (catabolism).

molar enthalpy of evaporation    →   molarna entalpija isparavanja

Molar enthalpy of evaporation (Δ_l ^gH) is a change of enthalpy during evaporation divided by molarity of a liquid, and is equal to the heat energy spent when the evaporation is conducted under constant pressure, Δ_l ^gH=Q.