CONTRIBUTIONS FROM THE RESEARCH LABORATORY OF PHYS- 

 ICAL CHEMISTRY OF THE MASSACHUSETTS INSTITUTE OF 

 TECHNOLOGY. — NO. 17. 



OUTLINES OF A NEW SYSTEM OF THERMODYNAMIC 



CHEMISTRY. 



By Gilbert Newton Lewis. 



Received July 10, 1907. 



In the rapid development of theoretical chemistry, in which the 

 two laws of energy have played so important a role, two thermody- 

 namic methods have been widely used. The first, employed by Gibbs, 

 Duhem, Planck, and others, is based on the fundamental equations of 

 entropy and the thermodynamic potential. The second, employed 

 by such men as van't Hoff, Ostwald, Nernst, and Arrhenius, consists 

 in the direct application to special problems of the so-called cyclic 

 process. 



The first method is general and exact, and has been a favorite with 

 mathematicians and physicists, those who were already familiar with 

 the use of the potential theory in mechanics. But unfortunately, ex- 

 cept in name there is little analogy between physico-chemical equi- 

 librium and the equilibrium in a mechanical system, and it is perhaps 

 for this reason that the method has failed to commend itself to the 

 majority of chemists. It must be admitted that it is the second 

 method to which we owe nearly all of the advances that have been 

 made during the last thirty years through the application of thermody- 

 namics to chemical problems, and which is now chiefly used by inves- 

 tigators and in the text-books of physical chemistry. 



Yet the application of this method has been unsystematic and often 

 inexact, and has produced a large number of disconnected equations, 

 largely of an approximate character. An inspection of any treatise on 

 physical chemistry shows that the majority of the laws and equations 

 obtained by the application of thermodynamics, are qualified by the 

 assumption that some vapor behaves like a perfect gas, or some solu- 



