Green chemistry, also known as sustainable chemistry, is a branch of science that focuses on creating chemical products and processes that produce the least amount of hazardous substances possible. Green chemistry is a specific strategy to direct advancements in the field, not necessarily a distinct branch of chemistry. Catalysis is the use of catalysts to quicken chemical reactions. When used to speed up reactions, catalysts are independent substances that don't change over time. For instance, potassium permanganate can be used to speed up the breakdown of hydrogen peroxide into water and oxygen gas.