thermodynamics

thermodynamics (thûr´mo-dì-nàm´îks), branch of science concerned with the nature of HEAT and its conversion into other forms of energy. Heat is a form of energy associated with the positions and motion of the molecules of a body. The total energy that a body contains as a result of the positions and the motions of its molecules is called its internal energy. The first law of thermodynamics states that in any process the change in a system's internal energy is equal to the heat absorbed from the environment minus the WORK done on the environment. This law is a general form of the law of conservation of energy (see CONSERVATION LAWS). The second law of thermodynamics states that in a system the entropy cannot decrease for any spontaneous process. A consequence of this law is that an engine can deliver work only when heat is transferred from a hot reservoir to a cold reservoir or heat sink. The third law of thermodynamics states that all bodies at absolute zero would have the same entropy; this state is defined as having zero entropy.

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