Process function

This article is about the mathematical concept used in thermodynamics. For the engineering indicator, see process variable.

See also: List of thermodynamic properties

A process function, process quantity, or a path function is a physical quantity that describes the transition of a system from an equilibrium state to another equilibrium state. As an example, mechanical work and heat are process quantities because they describe quantitatively the transition between equilibrium states of thermodynamic systems. It depends on the work done and how the state is reached.

Path functions depend on the path taken to reach one state from another. Different routes give different quantities. Examples of path functions include work, heat and length. In contrast to path functions, state functions are independent of the path taken.

See also

• State function
• Thermodynamics