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FREDERICK BARRY 
character of its effect upon the distribution of total energy in an 
isolated chemical system. It is now necessary to consider its influence 
upon speed of reaction and on chemical equilibrium; that is, upon 
relative intensities of chemical activity, in contrast with the relative 
differences in internal energies that characterize initial and final states. 
The former problem involved a comparison of energy changes 
taken as wholCvS — total energy changes; and for its analytical formula- 
tion the law of the conservation of energy sufficed. The present 
inquiry necessitates at the outset an application of the distinction 
already referred to, between that part of the total energy change which 
can appear only as gain or loss of heat, and that which may so appear, 
and yet which may under favorable conditions be converted completely 
into work. For the tendency of one or more substances by combina- 
tion or decomposition to form others is clearly not a function of the 
total energy difference between the two, but rather of that part t)f it 
which is capable of transformation not only into heat, but into the 
work of building up new systems out of old; of transformation not 
only into irregular molecular motions, but into new types of periodic 
motion or of stress between the interacting atoms. 
Successfully to investigate these phenomena, therefore, we must 
know how the free energy of a chemical system changes with rise or 
fall of temperature. This knowledge the second law of thermo- 
dynamics supplies. The quantitative formulation of this law, derived 
from an analysis of reversible processes acting through complete cycles, 
is (lo): 
fr - 1 
This statement, which has been confirmed by development from 
different conceptual premises, may be read: "The temperature coeffi- 
cient of the free energy developed in any isolated natural process 
{dA)/(dT) is equal to the heat absorbed in that process (Q) divided by 
the absolute temperature (T). The statement is rendered more 
intelligible if we combine it with a similar analytical formulation of 
the law of the conservation of energy in terms of the same quantities. 
If the corresponding diminution in the total energy in the system be 
represented by U, this law requires that (lo): 
U = A - Q; 
(III) 
