The use of chemistry within the field of engineering can broadly be divided into two main areas. The first area is concerned with the application of chemistry as the basis of power generating machinery, such as combustion engines, for example. Knowledge of chemistry and chemical reactions is required in the design and subsequent production of such power generating equipment. The second area of use is chemical engineering, where the main purpose is to transform raw materials into more valuable or useful forms. Chemical engineers use their knowledge of chemistry to design, improve and maintain processes involving chemical and/ or biological transformations for use within large scale manufacture.
Individual processes, such as distillation, filtration, etc, are known as unit operations. These unit operations consist of a combination of chemical reactions, momentum-, heat- and mass-transfer operations. Sets of unit operations are then put together in varying configurations with the purpose of chemical separation and/ or synthesis.
Chemical engineering design is subject to three underlying, primary physical laws, namely the conservation of mass, momentum and energy. Movements of energy and mass involved in a chemical process are evaluated by applying laws of energy and mass balances to all parts of equipment, unit operations and indeed an entire plant.

Principles of reaction kinetics, thermodynamics and fluid mechanics, as well as transport phenomena are all elements to be taken into consideration during this evaluation process. Technology now allows this process to be aided by complex software models, or process simulators, which are usually able to simulate a range of unit operations.
The line between chemistry and chemical engineering is continually becoming thinner. Modern chemical engineers are now using their knowledge of chemistry, mathematics and physics to develop (or design), implement and produce their ideas for a range of products; suitable for medical, aviation, space and military uses.