In science, Antoine Laurent Lavoisier (1743-1974) was a French chemist notable for his caloric theory, in which heat was hypothesized to be a fluid-like indestructible mass-less particle, called caloric, capable of causing expansion in bodies. This theory was developed in refutation of the older “phlogiston theory”, outlined in 1718 by German chemist George Stahl, in which heat was was hypothesized to be a fire-like element, having mass, called “phlogiston” that was contained within combustible bodies and released during combustion. [1]

Between 1768 and 1787, Lavoisier published over sixty papers leading to his theory of combustion. [3] His caloric theory of combustion found its way to the physicists of the world principally through the famous publication of this 1789 textbook Elements of Chemistry. [4] The heat-expansion work and theories of Dutch physician and chemist Herman Boerhaave, who previously in 1732 had written an influential chemist textbook titled Elements of Chemistry, were influential to Lavoisier.

Lavoisier was also key player in the early development of the science of thermochemistry, particularly for the 1782 construction and use of an ice-calorimeter, which together with French mathematician Pierre-Simon Laplace was used to determine the heat released in combustion reactions. He is also considered as one of the founders of modern chemistry, known for his experimental work on compounds, explanation of combustion, and help in devising a system of chemical nomenclature. One of the first chemists to adopt Lavoisier’s theories was Scottish chemist Joseph Black who taught them as early as 1784. [2]

Reaction energies
In 1782, Lavoisier discussed his views on the nature of the energies and forces involved in the dissolution of metals in acids, such as in the process of dissolving a metal in nitric acid. In commentary on the subject of “energies” of reaction, he states: [5]

“To know the energies of all these forces, to succeed in giving them numerical values, to calculate them, that is the goal which chemistry ought to propose to itself. Chemistry advances slowly, but it is not impossible that it may reach the goal. Meanwhile we are obliged to content ourselves with general considerations … I only hope that the reader of this memoir will apprehend the possibility of some day applying exact calculations to chemistry. But, before all, certain data must be obtained which will serve as a foundation, and it is to that subject I mean to devote myself.”

It was at least hundred-years before this goal began to be realized; specifically, with the development of the science of chemical thermodynamics, beginning in the 1870s, various physicists and chemists soon began to give insight into some of the numerical values of the types of energies involved in chemical reaction; such as: internal energy, entropy, enthalpy, free energy, activation energy, bond energy, etc.

Thermodynamics
In 1823, French physicist Sadi Carnot used Lavoisier's conception of caloric to outline a generalized theory of heat-engines, or of the production of motion by heat. In Carnot’s theory, the production of motion by heat was due to the need of bodies in contact to “re-establish equilibrium in the caloric”, such that the fall of the caloric from a hot body, through an intermediate substance, e.g. steam, to a colder body, thus causing expansion (and later contraction) in the “working substance”, was the drive or impelling power of the heat engine.

The subtle erroneous assumption implied in this theory is that in the cycle of the heat engine, in which (a) caloric particles are added to the working substance, (b) the working substance expands, (c) caloric particles are removed from the working substance, and (d) the body contracts to its original state, that “no permanent change occurs in the condition of the working body”.

In the late 1840s, German physicist Rudolf Clausius became aware of Carnot’s theory, through the work of French physicist Émile Clapeyron and English physicist William Thomson, and set out to amend Carnot’s assumption that the condition of the body never changes with the newer logic of the theory of heat in which heat is considered as the energy related to the vibratory motion or kinetic movement of particles, along with the mechanical equivalent of heat, in which the production of work by heat and heat by work are proportional, and thus, subsequently, a portion of heat is consumed by the particles of the working body as they act on each other in a cycle in an irreversible manner. As such, according to Clausius, the condition of the working body does change, and this change shows itself as a consumption of heat in the constituency of the working body as particles act or work on each other in an irreversible manner.

To quantify this internal work, in an approximate manner, Clausius developed the model of "entropy", in which the intensive quantity of heat dQ, passing into or out of the system, is divided by the extensive measure of absolute temperature T at the surface of the working body, and this quantity, dQ/T, is then said to model the energy workings of the system particles as they act on each other, and was called by Clausius the "transformation-content" of the working body. This was the start of the science of thermodynamics.

References
1. Brock, William H. (1993). The Norton History of Chemistry. New York: W. W. Norton.
2. Antoine Lavoisier (1743-1794) - History of Gas Chemistry, Bruce Mattson - Creighton University.
3. Partington, J.R. (1957). A Short History of Chemistry, 3rd ed. New York: Dover (reprint).
4. Lavoisier, Antoine. (1789). Elements of Chemistry, (pg. 5). London: G.G. and J.J. Robinsons.
5. (a) Lavoisier, Antoine. (1872). “Considerations Generales sur la Dissolution des Metaux dans les Acides”, Mem. De l’Acad. Des Sciences, pg. 492.
(b) Muir, Matthew M.P. (1907). A History of Chemical Theories and Laws (pg. 388). Wiley.

External links
● Antoine Lavoisier – Wikipedia.