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It has been suggested that Thermodynamic variable be merged into this article or section. (Discuss) |
A thermodynamic state is a set of values of properties of a thermodynamic system that must be specified to reproduce the system. Once a sufficient set of values of properties have been specified, values of all other properties of the system are uniquely determined. The number of values required to specify the state depends on the system and is not always known.
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Systems found in nature are often dynamic and complex, but in many cases their states are amenable to description based on proximity to ideal conditions. One such ideal condition is that of a stable equilibrium state. Based on many observations, thermodynamics postulates that all systems having no effect on the external environment will change in such a way as to approach unique stable equilibrium states.
A common example in which the state can be succinctly described is a closed simple system in an equilibrium state. A closed simple system is an ideal system devoid of any internal adiabatic, rigid, or impermeable boundaries and not being acted upon by any external force fields or inertial forces. Based on observation, scientists and engineers have postulated that the state of a simple system at equilibrium can be completely characterized by specifying two independent property variables, such as temperature and pressure, and the masses of the particular chemical species in the system. Relying on this postulate, for many chemical species, phase distribution and intrinsic phase properties such as density, heat capacity, thermal conductivity, viscosity, enthalpy, and entropy have been reproducibly measured and catalogued as functions of temperature and pressure.
