CHEMISTRY GLOSSARY

half-life of a reactant    →   poluživot reaktanta

For a given reaction the half-life, t_1/2, of a reactant is the time required for its concentration to reach a value that is the arithmetic mean of its initial and final (equilibrium) value.

Half-life is constant for first-order reactions.

Half-life is not constant for second-order reactions but rather it varies with initial concentration and k.

hydrogen    →   vodik

Hydrogen was discovered by Sir Henry Cavendish (England) in 1766. The origin of the name comes from the Greek words hydro and genes meaning water and generate. It is colourless, odourless gas, burns and forms explosive mixtures in air. Reacts violently with oxidants. Hydrogen is the most abundant element in the universe. Commercial quantities of hydrogen are produced by reacting superheated steam with methane or carbon. In lab work from reaction of metals with acid solutions or electrolysis. Most hydrogen is used in the production of ammonia and in metal refining. Also used as fuel in rockets. Its two heavier isotopes (deuterium and tritium) used respectively for nuclear fusion.

salt    →   soli

Salt is an ionic compound formed by the reaction of an acid and a base. The reaction of sodium hidroxide to hydrochloric acid gives sodium chloride

scavenger    →   čistači

Scavenger is a reagent that removes a trace component from a system or that removes a reactive intermediate from a reaction.

Schiff base    →   Schiffova baza

Schiff base is a class of compounds derived by the chemical reaction (condensation) of aldehydes or ketones with aromatic amines, for example

They were named after the German chemist Hugo Schiff (1834-1915).

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.

hydrolysis    →   hidroliza

Hydrolysis is a chemical reaction in which water reacts with another substance to form two or more new substances. This involves ionisation of the water molecule, as well as splitting of the compound hydrolysed, e.g.

Examples are conversion of starch to glucose by water in the presence of suitable catalysts and a reaction of the ions of a dissolved salt to form various products, such as acids, complex ions, 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.

substitution    →   supstitucija

Substitution (substitution reaction) is a reaction in which an atom or fragment within a molecule is replaced with another atom or a fragment.

substrate    →   supstrat

1. Substrate is a surface upon which an organism grows, sometimes by using chemicals of particles in the material as food

2. Substrate is a substance that is acted upon by an enzyme during a biochemical reaction.

3. Substrate is the material or product that is to be coated (for example, paint or laminate.).