A ChemicalProcess occurs whenever chemical compounds (CompoundSubstances) are formed or decomposed. For example, reactants disappear as chemical change occurs, and products appear as chemical change occurs. In a chemical change a chemical reaction takes place. Catalysts in a ChemicalProcess may speed up the reaction, but aren't themselves produced or consumed. Examples: rusting of iron and the decomposition of water, induced by an electric current, to gaseous hydrogen and gaseous oxygen.