CHEMISTRY GLOSSARY
thermodynamic equilibrium → termodinmička ravnoteža
Thermodynamic equilibrium is a system equilibrium in which energy that it gains from its surroundings is exactly balanced by the energy that it loses, no matter how much time is allowed to pass.
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 Kp and Kc 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 ΔrG°, the standard Gibbs free energy change in the reaction, by
thermodynamics → termodinamika
Thermodynamics is the scientific study of the interconversion of heat and other forms of energy.
fossil fuel → fosilno gorivo
Fossil fuels (coal, oil, and natural gas) are the fuels used by man as a source of energy. They are formed from the remains of living organisms and all have a high carbon or hydrogen content. They have value as fuels on the exothermic oxidation of carbon to form carbon dioxide
and the oxidation of hydrogen to form water
freon → freon
Freon (chlorofluorocarbon, CFC) a type of compound in which some or all of the hydrogen atoms of hydrocarbon (usually an alkane) have been replaced by chlorine and fluorine atoms. Most CFC are chemically uncreative and are stable at high temperatures. They are used as aerosol propellants, refrigerants, and solvents, and in the manufacture of rigid packaging foam. CFC because of their chemical inertness, can diffuse unchanged into the upper atmosphere. Here, photochemical reactions cause them to break down and react with ozone. For his reason, their use has been discouraged.
fuel cell → gorivi članak
Fuel cell is a device that converts chemical energy into electrical energy. It is different from a battery in that the energy conversion continues as long as fuel and oxidising agent are fed to the fuel cell; that is, in principle indefinitely. (A battery is manufactured with a limited amount of chemicals, and it is exhausted when all the chemicals have reacted.) It is a galvanic cell where spontaneous chemical reactions occur at the electrodes. The fuel is oxidised at the anode, and the oxidising agent (almost always oxygen or air) is reduced at the cathode. Presently, the most commonly used fuel is hydrogen. More conventional fuels (e.g., petrol or natural gas) must be converted (reformed) into hydrogen before they can be utilised in a fuel cell.
Some fuel cells employ an aqueous solution as electrolyte, that can be either acidic or basic (alkaline), or an ion-exchange membrane soaked in aqueous solution can act as the electrolyte. These fuel cells operate at relatively low temperatures (from room temperature to not much above the boiling point of water). Some fuel cells employ molten salts (especially carbonates) as electrolytes and have to operate at temperatures of several hundred degrees centigrade (Celsius). Others employ ionically conductive solids as electrolyte and must operate close to 1 000 °C.
galvanic celll → galvanski članak
Galvanic cell (voltaic cell) is a simple device with which chemical energy is converted into electrical energy. Galvanic cells consist of two separate compartments called half cells containing electrolyte solutions and electrodes that can be connected in a circuit. Two dissimilar metals (e.g., copper and zinc) are immersed in an electrolyte. If the metals are connected by an external circuit, one metal is reduced (i.e., gains electrons) while the other metal is oxidized (i.e., loses electrons).
In the example above, copper is reduced and zinc is oxidized. The difference in the oxidation potentials of the two metals provides the electric power of the cell.
A voltaic cell can be diagrammed using some simple symbols. In the diagram the electrodes are on the outer side of the diagram and a vertical line (|) is used to separate the electrode from the electrolyte solution found in the compartment. A double vertical line (||) is used to separate the cell compartments and is symbolic of the salt bridge. Usually in a diagram the species oxidized is written to the left of the double slash. Here is an example of the Daniell cell:
The names refer to the 18th-century Italian scientists Alessandro Volta (1745-1827) and Luigi Galvani (1737-1798).
gamma radiation → gama-zračenje
Gamma radiation is electromagnetic radiation of extremely short wavelength. Gamma radiation ranges in energy from about 10-15 J to 10-10 J (10 keV to 10 MeV) (wavelength less than about 1 pm). Gamma rays are emitted by excited atomic nuclei during the process of passing to a lower excitation state.
Gamma rays are extremely penetrating and are absorbed by dense materials like lead and uranium. Exposure to gamma radiation may be lethal.
Citing this page:
Generalic, Eni. "Energija aktivacije." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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