Chemical Reaction
. Chemical Reaction, process by which atoms or groups of atoms are redistributed, resulting in a change in the molecular composition of substances. An example of a chemical reaction is formation of rust (iron oxide), which is produced when oxygen in the air reacts with iron. The products obtained from a given set of reactants, or starting materials, depend on the conditions under which a chemical reaction occurs. Careful study, however, shows that although products may vary with changing conditions, some quantities remain constant during any chemical reaction. These constant quantities, called the conserved quantities, include the number of each kind of atom present, the electrical charge, and the total mass. See Chemical Symbols: Periodic Table of Elements In order to discuss the nature of chemical reactions, certain basic facts about chemical symbols, nomenclature, and the writing of formulas must first be understood. All substances are made up of some combination of atoms of the che