A general term used for the industrial manufacture of useful chemical products from raw materials through chemical, physical, or biochemical transformation. The transformation may involve a single step or many steps within unit operations such as mixing, reaction, and separation, in either batch or continuous forms of operation. A chemical process can be presented schematically as either a block flow diagram or as a process flow diagram. Block flow diagrams use blocks to represent the unit operations with arrows to represent the flows in and out, whereas process flow diagrams provide more detail of the unit operations and include process piping, the main items of equipment, control valves, and operational information such as temperature, pressure, and flows.