Quick Inexact differential - represented by the symbol δ, rather than d. Dependent on the process as well as the initial and final states.
Path function - the amount of work done during each process is not only a function of the end states of the process but depends on the path that is followed in going from one state to another.
Details
In the figure above, 1 and 2 represent different states. Also, A, B, and C represent separate processes that may be taken from state 1 to state 2. The lines corresponding to A, B, and C may be considered the paths that correspond to each process. The area under a curve, that is, of a–1–2–b–a, depends on the path that is chosen.
In thermodynamics, an inexact differential or imperfect differential is any quantity, particularly heatQ and workW, that are not state functions (a property of a system that depends only on the current state of the system, not on the way in which the system acquired that state), in that their values depend on how the process is performed. The symbol, δ indicates that Q and W are path dependent. In terms of infinitesimal quantities, the first law of thermodynamics is thus expressed as:
The symbol δ denotes a inexact, or path-dependent, differential. The symbol d denotes an exact, or path-independent, differential.
Both δ and d are used to indicate differential quantities, but δ is typically used for quantities (such as heat, work, and mass transfer) that are path functions and have inexact differentials, while d is used for quantities (such as properties) that are point functions and have exact differentials.
Quantities such as heat, work, and mass transfer are path functions and have inexact differentials.
Properties are point functions and have exact differentials.
