Chemical reactions (abiotic reactions) are “classical” chemical reactions that are not mediated by bacteria. They may include reaction processes such as precipitation, hydrolysis, complexation, elimination, substitution etc. that transform chemicals to other chemicals and potentially alter their phase/state (solid, liquid, gas, dissolved). Precipitation is the removal of ions from solution by the formation of insoluble compounds, . a solid-phase precipitate. Hydrolysis is a process of chemical reaction by the addition of water. Complexation is the reaction process by which compounds are formed in which molecules or ions form coordinate bonds to a metal atom or ion. Biodegradation (biotic reactions) is.