Thermodynamics: laws, systems, and branches

Definition and scope of thermodynamics

Thermodynamics is a branch of physics that studies heat, work, and temperature and how these quantities relate to energy, entropy, and the physical properties of matter and radiation. Its behavior is described quantitatively by the four laws of thermodynamics, which use measurable macroscopic variables, while microscopic explanations can be provided through statistical mechanics. The field is widely applied across science and engineering, including physical chemistry, biochemistry, chemical engineering, mechanical engineering, and even areas like meteorology. The scope of thermodynamics is organized around the analysis of thermodynamic systems and their surroundings. A system is a precisely defined region of the universe, and its properties are linked through equations of state; these properties can be combined to express internal energy and thermodynamic potentials, which help determine equilibrium conditions and spontaneous processes. Thermodynamics can model how systems respond to environmental changes and is used to study phenomena such as engines, phase transitions, chemical reactions, transport processes, and even black holes. The topic also distinguishes classical thermodynamics (mainly near-equilibrium systems) from extensions such as non-equilibrium thermodynamics and statistical thermodynamics, which connects macroscopic behavior to microscopic particle dynamics.

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Four laws of thermodynamics overview

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