CHEMISTRY GLOSSARY

graphite    →   grafit

Graphite is an allotrope of carbon. The atoms are arranged in layers as a series of flat, hexagonal rings. Graphite is a good conductor of heat and electricity. The layers cleave easily, making graphite useful as a solid lubricant. A process to make pure synthetic graphite was invented by the American chemist Edward Goodrich Acheson (1856–1931). The process consists of heating a mixture of clay (aluminum silicate) and powdered coke (carbon) in an iron bowl. The reaction involves the production of silicon carbide, which loses silicon at 4150 °C to leave graphite.

specific quantity    →   specifična veličina

Specific quantity is often convenient to express an extensive quantity (e.g., volume, enthalpy, heat capacity, etc.) as the actual value divided by mass. The resulting quantity is called specific volume, specific enthalpy, etc.

spontaneously combustible    →   samozapaljivi materijal

Spontaneously combustible materials are materials that can ignite without an external source of heat. Heat sufficient to reach the ignition temperature may be generated by reaction with oxygen in the air, by the absorption of moisture, from heat generated during processing, or even from radioactive decay.

system    →   sustav

System is the region under consideration, as distinguished from the rest of the universe (the environment). Systems may be separated from environments by boundaries that prevent the transfer of mass (a closed system), of heat (an adiabatic system), or of any energy (an isolated system). Systems that exchange mass with the environment are open systems.

halocarbon    →   halogenirani ugljikovodik

Halocarbon is a compound containing no elements other than carbon, one or more halogens, and sometimes hydrogen. The simplest are compounds such as tetrachloromethane (CCl₄), tetrabromomethane (CBr₄), etc. The lower members of the various homologous series are used as refrigerants, propellant gases, fireextinguishing agents, and blowing agents for urethane foams. When polymerized, they yield plastics characterized by extreme chemical resistance, high electrical resistivity, and good heat resistance.

hardness    →   tvrdoća

Hardness is the resistance of a material to deformation of an indenter of specific size and shape under a known load. This definition applies to all types of hardness scales except Mohs scale, which is a based on the concept of scratch hardness and is used chiefly for minerals. The most generally used hardness scales are Brinell (for cast iron), Rockwell (for sheet metal and heat-treated steel), Knoop (for metals).

hydration    →   hidratacija

Hydration is addition of water or the elements of water (i.e. H and OH) to a molecular entity. The term is also used in a more restricted sense for the process:

infrared radiation    →   infracrveno zračenje

Infrared radiation is an electromagnetic radiation within the area from 1.0 μm to 300 μm, and is responsible for the transmission of radiant heat.

thermit welding    →   termitno zavarivanje

Thermit welding is a group of welding processes in which fusion is produced by heating with superheated liquid metal resulting from a chemical reaction between a metal oxide and aluminium.

Hesse’s law    →   Hessov zakon

Hesse’s law says that reaction heat of some chemical change does not depend on the way in which the reaction is conducted, but only on starting and ending system state. Hesse’s law is also known as the law of constant heat summation. Hesse’s law is also known as the law of constant heat summation. The law was first put forward in 1840 by the Swiss-born Russian chemist Germain Henri Hess (1802-1850).

Hesse’s law can be used to obtain thermodynamic data that cannot be measured directly. For example, it is very difficult to control the oxidation of graphite to give pure CO. However, enthalpy for the oxidation of graphite to CO₂ can easily be measured. So can the enthalpy of oxidation of CO to CO₂. The application of Hess’s law enables us to estimate the enthalpy of formation of CO.

The equation shows the standard enthalpy of formation of CO to be -110 kJ/mol.