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Notes:
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Systems in conditions of equilibrium strictly follow the rules of thermodynamics (Callen,
1985). In such cases, despite the intricate behaviour of large numbers of molecules, the
system can be completely characterized by a few variables that describe global average
properties. The extension of thermodynamics to non-equilibrium situations entails the
revision of basic concepts such as entropy and its related thermodynamic potentials as well
as temperature that are strictly defined in equilibrium. Non-equilibrium thermodynamics
proposes such an extension (de Groot & Mazur, 1984) for systems that are in local
equilibrium. Despite its generality, this theory is applicable only to situations in which the
system manifests a deterministic behaviour where fluctuations play no role. Moreover, nonequilibrium
thermodynamics is formulated in the linear response domain in which the
fluxes of the conserved local quantities (mass, energy, momentum, etc.) are proportional to
the thermodynamic forces (gradients of density, temperature, velocity, etc.). While the linear
approximation is valid for many transport processes, such as heat conduction and mass
diffusion, even in the presence of large gradients, it is not appropriate for activated
processes such as chemical and biochemical reactions in which the system immediately
enters the non-linear domain or for small systems in which fluctuations may be relevant... |
