Sadi Carnot

Carnot sought to better understand the performance of the Cornish engine for the benefit of France. His ground-breaking analysis involved new theories on thermal efficiency, maximum work, and closed-cycle operation. Carnot proposed an ideal heat engine that achieved the best possible efficiency, regardless (surprisingly) of the nature of the working substance. Unfortunately, embedded deep inside Carnot’s powerful analysis was a single major flawed assumption: the caloric theory of heat in which heat is treated as a conserved quantity.

Caloric theory: beginning of its end

The early 1800s provided new evidence challenging the caloric theory when Rumford bored a cannon and boiled water, Davy melted ice by using friction, and Young made the connection between light and radiant heat. Mayer and Joule then succeeded in killing caloric by simply ignoring it and instead embracing work–heat equivalence.

Rudolf Clausius

Clausius completed the heat engine analysis that Carnot started by eliminating the caloric theory on which it was based and replacing it with Joule’s heat–work equivalence. He proceeded to validate Carnot’s theory of the irrelevance of the working substance’s nature by proving equivalent performances between an engine based an ideal gas and one based on liquid–vapor water. Clausius embraced two principles that became forerunners of the 1st and 2nd Laws of Thermodynamics: 1) heat–work equivalence, and 2) heat must flow from hot to cold whenever work is done in a cyclic process. He also introduced a new physical property of matter he named U, which later became known as internal energy. In his work, Clausius took the first major step towards completion of thermodynamics.

Lavoisier and the birth of modern chemistry

Building on the discoveries of such scientists as Priestley and Cavendish, Lavoisier invalidated the concept of phlogiston, discovered respiration to be a form of combustion, and ultimately laid the foundation for modern chemistry. Unfotunately, he also endorsed the caloric theory of heat, which was later proven to be incorrect.

William Thomson (Lord Kelvin)

Being raised on the caloric theory in which heat is a conserved quantity, Thomson faced challenges in accepting Clausius’ analysis of Carnot’s heat engine. Once he finally overcame these challenges, helped by collaborating with his brother James, Thomson accepted and then furthered Clausius’ work by proposing a different perspective of Clausius’ 2nd Principle and the 2nd Law of Tthermodynamics: energy dissipation. This chapter concludes with the role Hermann von Helmholtz played in bringing a rational approach to a thermodynamic science based on cause–effect.

O episódio histórico das teorias do flogisto e calórico: criando interfaces entre a História e Filosofia da Ciência e o Ensino de Química na busca pela humanização do trabalho científico.c

ResumoA análise de episódios da história da ciência pode ser usada como uma estratégia didática que promove a superação de visões descontextualizadas da ciência. Permitindo que os alunos vivenciem a construção do conhecimento científico e percebam que eles não são feitos a partir de lampejos de genialidade ou de maneira isolada. Tornando-se impossível elencar apenas um indivíduo para representar a formulação de uma lei ou teoria. Neste trabalho nosso objetivo é apresentar a contribuição de Lavoisier no episódio histórico sobre o abandono da teoria do flogisto e ascensão da teoria do calórico, salientando a importância dada a experimentação no século XVII e XVIII e buscando com isto nos livrar de narrativas anedóticas, descontextualizadas e elitistas ainda presentes no Ensino de Química que colocam este personagem como pai da química moderna.Palavras-chave: História e Filosofia da Ciência; Ensino de Química; Lavoisier.AbstractThe analysis of episodes of the history of science can be used as a didactic strategy that promotes the overcoming of decontextualized visions of science. This makes the students experience the construction of scientific knowledge and realize that they are not made from glimpses of genius or in an isolated way, being impossible to list only an individual to represent the formulation of a law or theory. In this work, our objective is to present the real contribution of Lavoisier in the historical episode about the phlogiston theory abandonment and the rise of the caloric theory. From this, it is possible to stress the importance given to experimentation during the 17th and 18th century, seeking to get rid of anecdotal, decontextualized and elitist narratives that are still present in the Teaching of Chemistry that put this personage like father of the modern chemistry.Keywords: History and Philosophy of Science; Chemistry teaching; Lavoisier.