Wärmesatz

Wärmesatz (literally "heat law") is a historical German term used to denote a family of principles concerning heat and energy exchange in thermodynamic systems. Rather than a single formal postulate, Wärmesatz appears in some 19th- and early 20th-century literature as an umbrella label for the body of thermodynamics, with its exact content varying by author.

In modern physics, the term is uncommon and not part of standard nomenclature. When used, it typically serves as an informal or pedagogical label for foundational ideas about heat transfer, energy conservation, and the emergence of irreversibility, rather than a precise, universally defined theorem.

Core ideas associated with Wärmesatz include the direction of heat flow (heat tends to move from hotter to cooler bodies), the conservation of energy in processes that involve heat and work (first law), and the increase of entropy in spontaneous processes (second law). Some formulations echo the Kelvin–Planck and Clausius statements, while others present broader, less formal statements about energy-entropy balance.

Relation to established terms: In contemporary texts, the explicit names of the laws—First, Second (and Third) Law of Thermodynamics, along with the Kelvin–Planck and Clausius statements—are preferred over the umbrella term Wärmesatz.

See also: Thermodynamics, Heat transfer, Entropy, First law of thermodynamics, Second law of thermodynamics, Kelvin–Planck and Clausius statements.