Principle of maximum work

Similar considerations were advanced by M. Berthelot (1805), and this so-called Principle of Maximum Work found its way in some form or other, into all chemical treatises. The following, among other, objections were later brought against it ... 

From Pierre Duhem, Traite elementaire de mecanique chimique fondee sur la thermodynamique, 2 vols. (Paris Hermann, 1897), I vi. The doctoral thesis, Lepotentiel thermodynamique et ses application a la mecanique chimique et a la theorie des phenomenes electriques (1886), was rejected, partly because of its criticism of the "principle of maximum work" developed by the influential Collee de France chemist Marcellin Berthelot. 

Analogous considerations lead to the conclusion that the reverse must be true at high temperatures. Both conclusions are most completely verified by experience. Indeed a law was stated by Thomsen, and especially by Berthelot —by the latter under the name of the principle of maximum work — that all chemical reactions which take place of their own accord are accompanied by evolution of heat. 

Very intense reactions principle of maximum work — Let us now consider the case, the opposite of the preceding, in which the modification studied is of great intensity the difference (TT —TF )i which is always positive, has a very great value it therefore gives its sign to the quantity Q. Whence the foUowing proposition ... 

In 1854 J. Thomsen stated the following proposition, which Berthelot has called the Principle of Maximum Work ... 

The principle of maximum work may not even be regarded as a principle applicable to all chemical reactions at a fixed temperature, caibonate of calcium dissociates, hydrogen reduces magnetic iron oxide, in spite of the fact that these reactions absorb heat we might cite an immense number of exceptions to the principle of maximum work, all chosen from among reactions of feeble intensity. 

The principle of maximum work should therefore be limited to reactions of great intensity, for which it is applicable from the preceding deductions. 

A compound formed with absorption of heat cannot, according to the principle of maximum work, be formed in a direct and isolated manner but an endothermic compound may be formed if its formation is the necessary consequence of reactions whose ensemble corresponds to a liberation of heat. 

Consequence relative to very low temperatures the principle of maximum work is exact at these temperatures.— Let... 

For the thermochemists who accepted without restriction the principle of maximum work an exothermic reaction was one susceptible of producing itself an endothermic reaction could not take place without the aid of external energy. 

As the temperature is raised higher and higher, we see increase the number of reactions, decompositions of exothermic compounds, or syntheses of endothermic compounds which are exceptions to the principle of maximum work. According to the happy ex ... 

Systems with unlimited reaction and the principle of maximum work.—A considerable number of chemical reactions are classed in the category of which the formation of sulphuretted hydrogen and the decomposition of silicon trichloride are types. All these reactions give rise to an important observation At tent -peratures indvded between t and r, when the ordy possible reaction is limited by stales of false equiltbriumy and at temperatures between r and 6, where this reaction is unlimited, it is exothermic, so that the principle of maximum work is verified to find the principle of maximum work in default it is necessary to attain temperatures, above 0, where states of veritable equilibrium may be established. 

Stability of equilibrium, 96.—8a. Interpretation of the non-compensated work, 97.—83. Intensity of reaction slow reactions, 98.-84. Very intense reactions principle of maximum work, 99.—... 

X40. Corollary to this law, 165.—X4X. Consequence relative to very low temperatures the principle of maximum work is exact at these temperatures, 165.—X42. Consequence for high temperatures, 166.—... 

Case of reactions which neither absorb nor liberate heat, 210.—X79. Phenomena of etherification, 210.—x8o. Minimum dissociation of hydrogen selenide, 211.—x8x. Similarity of the preceding principle and Moutier s law. At very low temperatures the principle of maximum work is exact, 212. 

Silicon trichloride. Investigations of Troost and Haute-feuille, 890.—293. Systems with unlimited reaction and the principle of maximum work, 891.—294. Systems with unlimited reaction are not essentially distinct from systems with limited reaction, 891. —295. One may always cool a chemical system sufficiently for it to exist in the state of false equilibrium, 898.-296. False equilibria at very low temperatures. Pictet s researches, 898.—297. The reaction point, 894.—298. Reaction point in the phosphorescence of phosphorus, 896.—299. Analogy of the states of false equilibria with the mechanical equilibria due to friction, 898.—300. The existence of false equilibria in chemical i stems is not exceptional but regular,... 

In their endeavours to measure chemical forces by means of thermal quantities, Berthelot and Thomsen were undoubtedly guided by the law of the conservation of energy, but the principle of maximum work is by no means a necessary consequence of this law. The first law merely states that the (positive or negative) heat evolved in a chemical reaction is equal to the change in energy of the transformed substances. Under what conditions the reaction will take place or fail to take place is a question which it is beyond the scope of the first law of thermodynamics to decide. The direction in which an energy change will proceed can only be determined with the aid of the second law of thermodynamics. 

Berthelot was aware that some reactions occur spontaneously with absorption of heat, but he supposed that here foreign energies were involved. He later restricted the principle of maximum work (although heat was really used instead of work ) to reactions between solids, when it is approximately correct, and defined chemical heat, to which the principle applies, as that transformable into work, which is really free energy (see below). 

Bertholet Principle of Maximum Work n Of all possible chemical processes which can proceed without the aid of external energy, that process which always takes place is accompanied by the greatest evolution of heat. This law holds good for low temperatures only and does not account for endothermic reactions. (Russell JB (1980) General chemistry. McGraw-Hill, New York)... 

Berthelot Marcelin (1827-1907) Fr. chem., enunciated the principle of maximum work, known for his sharp criticism ( Essai de mecanique chimique fondee sur la thermochimie 1879)... 

---