In thermodynamics, equivalence-value, from the German Aequivalenzwerth, is the mathematical value of a transformation, of heat into work or work into heat, defined by the ratio of the quantity of heat Q, interring or leaving a system, and the absolute temperature T of the surface of system, where the heat enters or leaves: [1]

$\frac{Q}{T}$

The term and logic behind the term were developed in 1854 by German physicist Rudolf Clausius, which is a precursory synonym for the 1865 quantity of entropy, being built on the phenomenon of the mechanical equivalent of heat in relation to its effect inside of working body during a cycle. [2]