Thermodynamic equilibrium

In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann distribution. This allows a single temperature to be attributed to the system. The key idea is that the macroscopic parameters are unchanging. The term "thermal equilibrium" is also used to describe this situation.

Related Topics:
Thermodynamics - Thermodynamic system - Energy distribution - Maxwell-Boltzmann distribution - Temperature

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The process that leads to a thermodynamic equilibrium is called thermalisation. An example of this is a system of interacting particles that is left undisturbed by outside influences. By interacting, they will share energy/momentum among themselves and reach a state where the global statistics are unchanging in time.

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Local thermodynamic equilibrium (LTE) occurs when massive particles are all in thermal equilibrium with each other (i.e. they may all be described by a single temperature) but the electromagnetic radiation field is not thermally equilibrated. A thermally equilibrated radiation field would have a black body distribution at the same temperature as the massive particles. The fact that the massive particles are equilibrated offers a great simplification in the calculation of the system properties, while allowing for more complex types of electromagnetic radiation to be described.

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