Chemical and Physical Changes

In API manufacture, whether via chemical synthesis, rDNA technology, or extraction from natural products, there are significant changes (physical and chemical) from the starting materials to the API. In the formulation process, however, the quality and specifications of the API are retained. The addition of excipients to produce the drug product in a finished dosage form does not present physical or chemical changes to the API. 

For the most part, experimental observations made by chemists—of phase changes, physical and chemical properties, chemical reactions, and so on—are averaged outcomes resulting from the behaviors of a very large number of interacting particles, such as molecules, ions, or rare gas atoms. To make sense of these observations, two general approaches have been pursued. 

Matter can undergo two kinds of changes—physical and chemical. Physical changes in a substance affect only physical properties, such as its size and shape, or whether it is a solid, liquid, or gas. For example, when water freezes, its physical state changes from liquid to solid, but it s still water. 

Matter can undergo two kinds of changes— physical and chemical. A physical change affects the physical properties. When a chemical change takes place, a new product is produced. How can a scientist tell if a chemical change took place ... 

Discussion of phases and miscibility requires a proper definition. The general thermodynamic definition of a phase states that a phase is a region of constant or continuously changing physical and chemical properties, the state of which can be described by thermodynamic relations. 

Some relatively pure liquids recovered from the environment can be distilled or rereflned and reused. For example, petroleum products recovered from some waste sludge by thermal desorption or waste oils collected from automobiles can be rerefined to make a usable product. The potential to recover usable product from material spilled into the environment can be limited, however. Once spilled, a solvent or petroleum product begins to change physically and chemically. The liquid can become contaminated with water, dirt, or other substances. After some time, chemical and biochemical reactions will alter the chemical composition of the material. Further, the volume recovered from spill cleanup may be relatively small and a rereflning facility may not be located nearby. As a result, it may be more feasible simply to ship the waste for energy recovery. 

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