History of thermodynamics

The development of ideas about heat, work, energy, and entropy, from early caloric theories to classical thermodynamics and statistical mechanics.

Caloric theory: An obsolete theory that treated heat as a conserved, weightless fluid called caloric. It framed heat as material before experiments established its connection to work and energy.
First law of thermodynamics: The principle that energy is conserved while heat and work transfer energy across system boundaries. It formalized the conversion between heat and work developed through nineteenth-century experiments.
Rudolf Clausius: A German physicist who formulated the second law and introduced the modern concept of entropy. He gave the second law its influential general formulation and named entropy.
Statistical mechanics: A framework that derives macroscopic physical behavior from the statistics of microscopic states. It recast thermodynamic laws as statistical regularities rather than separate empirical rules.
Chemical thermodynamics: The application of thermodynamic principles to chemical reactions, mixtures, and phase changes. It extended the laws from heat engines to chemical equilibrium and reaction direction.
Steam engine: A heat engine that converts energy from steam into mechanical work. Its practical limits prompted questions about heat, efficiency, and useful work.
Second law of thermodynamics: The principle that natural processes have a direction constrained by nondecreasing total entropy. It explains why energy conservation alone cannot determine which processes occur spontaneously.
William Thomson, 1st Baron Kelvin: A British mathematical physicist who developed the absolute temperature scale and helped formulate thermodynamics. His work established an absolute temperature scale and advanced the laws' formulation.
Kinetic theory of gases: A theory explaining gas properties through the motion and collisions of microscopic particles. It provided a microscopic account of heat and pressure that challenged purely macroscopic descriptions.
Free energy: A thermodynamic potential that measures the work available from a system under specified conditions. Free-energy concepts translated thermodynamic laws into practical criteria for work and spontaneous change.

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Rankine scaleRelated: Absolute temperature scales emerged alongside the formal development of thermodynamics.