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Le Chatelier's Principle - Henri-Louis Le Chatelier - Friedrich Wilhelm Oswald.. Thermodynamics - Heat of Matter - 1848 to 1914

Le Chatelier's Principle

Henri-Louis Le Chatelier

While studying problems involving high temperatures, such as mining disasters and the cement industry, Le Chatelier discovered that adding or subtracting heat from an equilibrium causes it to deviate. When Le Chatelier was in his early thirties—in the early 1880s—he summarized these observations in what is now known as Le Chatelier's Principle: When a factor acts on a system in equilibrium, the system adjusts itself in the direction that absorbs this effect. This factor may be matter—as originally observed by Berthollet on the shores of the salt lakes of Egypt—or heat, as now established by Le Chatelier.

The benefits of this principle to chemistry are numerous. The chemist can now infer whether a reaction will occur spontaneously using the Gibbs function. He can also manipulate the reaction to move it in the desired direction using Le Chatelier's principle.

This principle can be visualized as two players balancing on either end of a seesaw with a set of balls. If one player drops some balls, the other player must also throw some balls to maintain balance on either end of the seesaw. A balanced chemical reaction is like a seesaw: removing one product causes the reaction to shift, producing more of that product. If the reaction is strongly exothermic (a word introduced at that time to describe reactions that produce heat), cooling it will remove this heat and cause the reaction to produce more products and heat.

Le Chatelier found Gibbs's class rule particularly useful in his research on metallurgy (Le Chatelier himself derived some parts of the class rule using his own principle of equilibrium), most of which appeared in the Journal of Metallurgy, which he and his daughters published. Le Chatelier also used his principle in his research as a consultant on shell casings—a position he held during the spontaneous detonation, entropy, and energy waste known as World War I.

In the midst of this war, with the growing hostility between France and Germany, Gibbs's work had to be translated into German to be accepted by all. Fortunately for Gibbs, one of his heroes was a German: Friedrich Wilhelm Oswald.

Friedrich Wilhelm Oswald

Friedrich Wilhelm Oswald was initially an average student, preferring to spend his time collecting insects, photography, woodworking, and making fireworks. However, he eventually became one of the most influential scientists of his time. His interests at college included music, drawing, socializing with his classmates, and generally extolling romanticism. After receiving a warning from his father, his academic performance improved, and in the early 1880s, he became a professor of chemistry.

Oswald saw the usefulness of thermodynamics and the phase equivalence principle in chemistry and taught them to his students. In fact, Oswald became so convinced of the benefits of chemical theory, and the promise of the marriage of physics and chemistry, that he founded the new science of physical chemistry. He began publishing the first journal in this field, the German Journal of Physical Chemistry, in the late 1880s. He long rejected atomic theory—referring to it as “atomic hypotheses” (13)—and debates raged between followers of both Oswald and Boltzmann. However, many chemists at the time saw no logic in these arguments. For them, considering matter as composed of atoms and heat as a movement was the desired starting point. Organic chemists did not wait for physical chemists to arrive at this conclusion; they continued working.