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Thermodynamics, division of physics concerned with the interconversion of heat, work, and other forms of energy, and with the states of physical systems. Classical thermodynamics is basic to engineering, parts of geology, metallurgy, and physical chemistry. Building on earlier studies of temperature and heat, Sadi Carnot pioneered the science with his investigations of the cyclic heat engine (1824), and in 1850 Rudolf Clausius stated the first two laws. Thermodynamics was further developed by J.W. Gibbs, H.L.F. von Helmholtz, Lord Kelvin, and J.C. Maxwell.

In thermodynamics, a system is any defined collection of matter: a closed system is one that cannot exchange matter with its surroundings; an isolated system can exchange neither matter nor energy. The state of a system is specified by determining all its properties, such as pressure, volume, etc. A process is a change from one state to another, the path being specified by all the intermediate states. A state function is a property or function of properties that depends only on the state and not on the path by which the state was reached.

See also: Physics.

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