Resumen de Clausius et la chaleur: le passage dissimulé de la substance à l'algèbre
Still nowadays, no one algebraic definition of heat is taught. Although anybody can easily make is own idea about heat, this non-regular lack, from the point of view of theoretical physics, can be explained by an historical consideration on the creation by Clausius of internal energy. In 1850, Clausius publishes On the Moving Force of Heat in which internal energy and entropy are created in order to make thermodynamics an entirely mathematical science. At the beginning, Clausius deny to Carnot that heat could be a conserved quantity, then, considering an ideal gas in a thermodynamical cycle, he shows that the conserved quantity cannot be heat, but another one, made by Clausius and called later "internal energy" by himself too. The main point of his demonstration is that the elementary quantity δQ cannot be an exact differential. Of course, a so important conclusion has several great consequences about thermodynamics in general. Firstly, internal energy becomes the new main quantity in thermodynamics, secondly, heat can be defined as the internal energy variation not due to mechanical work. Moreover, what is called "first principle of thermodynamics" can be seen as a simple consequence of this heat definition.
