CHEMISTRY GLOSSARY

enthalpy    →   entalpija

Enthalpy (H) is a thermodynamic property of a system defined by

where U is the internal energy of the system, p its pressure, and V its volume. J.W. Gibbs put the concept of an ensemble forward in 1902. In a chemical reaction carried out in the atmosphere the pressure remains constant and the enthalpy of reaction (ΔH), is equal to

For an exothermic reaction ΔH is taken to be negative.

enzyme    →   enzim

Enzyme is a protein that acts as a catalyst in biochemical reactions. Each enzyme is specific to a particular reaction or a group of similar reactions. Many require the association of certain nonprotein cofactors in order to function. The molecule undergoing a reaction (the substrate) binds to a specific active site on the enzyme molecule to form a short-lived intermediate: this greatly increases (by a factor of up to 10²⁰) the rate at which the reaction proceeds to form the product.

ester    →   ester

Esters are organic compounds formed by a reaction between alcohol and acids. Esters formed from carboxylic acids have the general formula RCOOR’. Triesters, molecules containing three ester groups, occur in nature as oils and fats.

Euler number    →   Eulerova značajka

Euler number (Eu) is a dimensionless quantity used in fluid mechanics, defined by

where p is pressure, ρ is density, and v is velocity.

reactivity series    →   reaktivni niz

Reactivity series or activity series is a series of elements (usually metals) ranked by their reactivity degree, made for comparison of reactions of elements with other substances, e.g. acids and oxygen.

reagent    →   reagens

Reagents are any substance used in a chemical reaction to detect, measure, examine, or produce other substances.

redox    →   redoks

Redox is a short form of the term for oxidation-reduction.

refractive index    →   indeks loma

For a non-absorbing medium, refractive index (n) is the ratio of the velocity of electromagnetic radiation (light) in vacuum to the phase velocity of radiation of a specified frequency in the medium.

reversible cell    →   povrativi članak

Reversible cell is an electrical cell the chemical action in which can be reversed by passing through it a current opposite in direction to that generated by the cell.

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