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When it is completely settled, so that macroscopic change is no longer detectable, it is in its own thermal equilibrium. It is not implied that it is necessarily in other kinds of internal equilibrium. For example, it is possible that a body might reach internal thermal equilibrium but not be in internal chemical equilibrium; glass is an ...
A prime example of this irreversibility is the transfer of heat by conduction or radiation. It was known long before the discovery of the notion of entropy that when two bodies, initially of different temperatures, come into direct thermal connection, then heat immediately and spontaneously flows from the hotter body to the colder one.
A few different types of equilibrium are listed below. Thermal equilibrium: When the temperature throughout a system is uniform, the system is in thermal equilibrium. Mechanical equilibrium: If at every point within a given system there is no change in pressure with time, and there is no movement of material, the system is in mechanical ...
An equilibrium state is mathematically ascertained by seeking the extrema of a thermodynamic potential function, whose nature depends on the constraints imposed on the system. For example, a chemical reaction at constant temperature and pressure will reach equilibrium at a minimum of its components' Gibbs free energy and a maximum of their entropy.
Classical thermodynamics deals with states of dynamic equilibrium.The state of a system at thermodynamic equilibrium is the one for which some thermodynamic potential is minimized (in the absence of an applied voltage), [2] or for which the entropy (S) is maximized, for specified conditions.
If it is defined that a thermodynamic system is in thermal equilibrium with itself (i.e., thermal equilibrium is reflexive), then the zeroth law may be stated as follows: If a body C, be in thermal equilibrium with two other bodies, A and B, then A and B are in thermal equilibrium with one another. [8]
The relation is generally expressed as a microscopic change in internal energy in terms of microscopic changes in entropy, and volume for a closed system in thermal equilibrium in the following way. d U = T d S − P d V {\displaystyle \mathrm {d} U=T\,\mathrm {d} S-P\,\mathrm {d} V\,}
The behavior of a thermodynamic system is summarized in the laws of Thermodynamics, which concisely are: . Zeroth law of thermodynamics; If A, B, C are thermodynamic systems such that A is in thermal equilibrium with B and B is in thermal equilibrium with C, then A is in thermal equilibrium with C.