CHEMISTRY GLOSSARY

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    →   disocijacija

Dissociation is the process by which a chemical combination breaks up into simpler constituents as a result of either added energy (dissociated by heat), or the effect of a solvent on a dissolved polar compound (electrolytic dissociation). It may occur in the gaseous, solid, or liquid state, or in a solution.

An example of dissociation is the reversible reaction of hydrogen iodide at high temperatures

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

ecological footprint    →   ekološki otisak

The Ecological Footprint is defined as the area of productive land and water ecosystems required to produce the resources that the population consumes (food, fiber, timber, energy, and space for infrastructure) and assimilate the wastes that the population produces (CO₂ is the only waste product currently included), wherever on Earth the land and water is located. It compares actual throughput of renewable resources relative to what is annually renewed. Non-renewable resources are not assessed, as by definition their use is not sustainable.

Ecological footprints and biocapacity are expressed in global hectares (gha). Each unit corresponds to one hectare of biologically productive space with world average productivity. In U.S. Footprint results are often presented in global acres (ga). One U.S. acre is equal to 0.405 hectares.

Humanity is currently consuming renewable resources at a faster rate than ecosystems can regenerate them and continuing to release more CO₂ than ecosystems can absorb. In 2007, humanity's Footprint was 18 billion gha, or 2.7 gha per person. However, the Earth's biocapacity was only 11.9 billion gha, or 1.8 gha per person. This represents an ecological overshoot of 50 per cent. Put another way, people used the equivalent of 1.5 planets to support their activities (more developed countries generally make higher demands on the Earth's ecosystems than poorer, less developed countries).

Einstein equation    →   Einsteinova jednadžba

Einstein equation is the mass-energy relationship introduced by Albert Einstein in 1905 in the form E = mc², where E is a quantity of energy, m its mass, and c is the speed of light. It presents the concept that energy possesses mass.

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.