Chemical substances

thumb|upright|A bottle of olive oil used in food

matter of constant composition best characterized by the entities (molecules, formula units, atoms) it is composed of and characterized by physical properties like density

thumb|A self-propelled crop sprayer spraying pesticide on a field thumb|A crop-duster spraying pesticide on a field Pesticides are substances that are used to control pests. They include herbicides, insecticides, nematicides, fungicides, and many others (see table). The most common of these are herbicides, which account for approximately 50% of all pesticide use globally. Most pesticides are used as plant protection products (also known as crop protection products), which in general protect plants from weeds, fungi, or insects.

A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by undesirable chemical changes. In general, preservation is implemented in two modes, chemical and physical. Chemical preservation entails adding chemical compounds to the product. Physical preservation entails processes such as refrigeration or drying. Preservative food additives reduce the risk of foodborne infections, decrease microbial spoilage, and

thumb|Ingredients for short rib soup

chemically identical molecular entities that can have the same set of molecular energy levels

The dihalomethanes are organic compounds in which two hydrogen atoms in methane are replaced by halogen atoms. They belong to the haloalkanes, specifically the subgroup of halomethanes, and contains ten members.