Tilstandsfunktion

Tilstandsfunktion (state function) is a property of a physical system that depends only on the current state of the system, not on the path by which the system arrived at that state. In thermodynamics, state functions are functions of state variables such as temperature, pressure, volume, and chemical composition. They contrast with path-dependent quantities like heat and work, which depend on the process path.

Formally, a state function has the property that the change between two states is independent of the process taken. The differential dF is an exact differential: there exists a scalar function F such that dF = (∂F/∂x)dx + (∂F/∂y)dy + … . This implies that the line integral of dF along any path between the same states yields the same value.

Common examples in thermodynamics are internal energy U, enthalpy H, entropy S, Helmholtz free energy F, and Gibbs free energy G. These quantities depend on state variables (for example U = U(S,V) or H = H(S,P)), and their changes can be determined from measurements of the state variables alone, without specifying the path.

In physics and chemistry, state functions are used to characterize equilibrium properties and to derive relationships such as Maxwell relations and fundamental thermodynamic equations. The concept extends to statistical mechanics, where macroscopic state functions emerge from ensembles and microscopic states. Understanding tilstandsfunktion helps distinguish intrinsic properties of a system from the history or process by which the system reached its current condition.