INFLUENCE OF TEMPERATURE ON CHEMICAL REACTION 217 
reactions are self-sustaining, whereas endothermal reactions are self- 
limiting, unless they be maintained by a persistently high environ- 
mental temperature. 
From the van t'Hoff equation another simple deduction of par- 
ticular interest may be made. If the heat of reaction, Z7, is zero, then 
the temperature coefficient of the equilibrium constant will equal 
zero: that is, K will be independent of the temperature. This condi- 
tion is approximated in the case of most physiological reactions, as 
has been remarked (lo). 
The influence of temperature on the velocities of reactions ap- 
proaching equilibrium cannot be determined in any manner analogous 
to that by which its influence on the equilibrium itself has been so 
successfully formulated; for thermodynamical method concerns itself 
with the description of final states, and not with the progress of phe- 
nomena in time. We might nevertheless hope to gain some insight 
into the nature of this influence by means of the relationship estab- 
lished by the Guldberg-Waage equation : namely, that the equilibrium 
constant for any reaction is equal to the ratio of the velocity constants 
of the two opposing reactions which establish the equilibrium. In 
the terms of the formulation used above, ^1/^2 = K. The variability 
of K with change of temperature having been formulated, the problem 
defines itself as an inquiry into the simultaneous variations of ki and 
k2 as the reaction approaches equilibrium; since during its course, 
the velocity at any instant is proportional to the difference between 
these values. This difference, unlike the corresponding ratio, is 
directly dependent upon the actual magnitudes of the velocity con- 
stants. Consequently, the first necessary step in the inquiry is to define 
the meaning of these figures. 
It is clear, in the first place, that they include all factors of varia- 
tion that affect the course of the reaction, save the concentrations 
alone. What are these factors? Primarily, of course, the speed of 
a reaction in either direction will be proportional to the driving force, 
to that which we call the chemical affinity between the reacting sub- 
stances. This, we know, is measurable by the free energy change in 
the process, which must be considered as determined by the specific 
characters of the interacting substances, and by these alone. This 
free energy is known from thermodynamical reasoning to be pro- 
portional to RTlnK (where these symbols have the meanings pre- 
