Definition of green chemistry. Green chemistry is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, use, and ultimate disposal.The twelve principles of green chemistry are: Prevention. Preventing waste is better than treating or cleaning up waste after it is created. Atom economy.Examples include the manufacture of ammonia, the manufacture of methanol and the manufacture of ethene. Some reactions use water as a solvent, for example in the manufacture of inorganic compounds such as hydrogen peroxide, phosphoric acid, sodium carbonate, and organic compounds such as ethane-1,2-diol and ethanol.