CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



THE DEVELOPMENT AND APPLICATION OF A GEN- 

 ERAL EQUATION FOR FREE ENERGY AND 

 PHYSICO-CHEMICAL EQUILIBRIUM. 



By Gilbert Newton Lewis. 



Received June 5, 1899. Presented by T. W. Richards, Juue 14, 1899. 



Introduction. 



The advance of modern physical chemistry has been largely clue to 

 the application to physico-chemical problems of the first and second laws 

 of thermodynamics and the gas law, — the latter both directly and by 

 analogy. Upon this basis the whole theoretical treatment of chemical 

 equilibrium rests at present. For this reason it may not be without 

 interest to attempt to express the relations deduced from these laws in a 

 single equation, the most convenient and the most general possible, which 

 may serve to systematize a part of our present knowledge, and perhaps 

 jjoint out new laws. Such an attempt will be made in this paper. 



I. General Equations of Free Energy and Equilibrium. 



The simplest expression embodying the first and second laws of ther- 

 modynamics is, 



A=T d / T+ C7, (1) 



where A is the diminution in free energy (Helmholtz) of a system in any 

 isothermal process ; U is the diminution in internal energy in the same 



_, , d A ii- 



process ; T is the absolute temperature ; -t-j=, represents the change in 



A as the temperature of the process varies, — the system changing in 

 every case from the same initial to the same final volume. 



A, the diminution of free energy, is a quantity which denotes the max- 

 imum amount of work obtainable in an isothermal process, and which is 

 determined definitely by the initial and final states of a system. It may, 



