text: In thermodynamics and thermal physics, the Gouy-Stodola theorem is an important theorem for the quantification of irreversibilities in an open system, and aids in the exergy analysis of thermodynamic processes. It asserts that the rate at which work is lost during a process, or at which exergy is destroyed, is proportional to the rate at which entropy is generated, and that the proportionality coefficient is the temperature of the ambient heat reservoir. In the literature, the theorem often appears in a slightly modified form, changing the proportionality coefficient.
  The theorem is named jointly after the French physicist Georges Gouy and Slovak physicist Aurel Stodola, who demonstrated the theorem in 1889 and 1905 respectively. Gouy used it while working on exergy and utilisable energy, and Stodola while working on steam and gas engines.