INFLUENCE OF TEMPERATURE ON CHEMICAL REACTION 209 
ical change: "The temperature coefficient of a heat of reaction is equal 
to the difference between the heat capacity of the reacting system 
before and after the change; is equal, in other words, to the difference 
between the heat capacities of the factors and the products of the 
reaction." This difference will, of course, be proportional to the 
mean specific heats of the substances in question.^ 
According to the interpretation of specific heat already suggested, 
this result, independently developed, might have been anticipated from 
molecular-kinetic considerations. The generalization thus possesses 
a certain interest, as an instance of the manner in which these two 
points of view — the thermodynamical and the atomistic — give each 
other mutual support. Its practical value lies in this: that by its 
means we may anticipate the probable magnitude of the temperature 
influence on heat of reaction, by knowledge of the easily measured 
specific heats of the reacting substances, and of those which are 
formed in the process. 
This influence of temperature is usually not great ; though in some 
single instances it is sufficient to cause reactions which are exothermal 
at low temperatures to become markedly endothermal at higher 
Such effects are of course observed only in those cases in which the 
specific heats of factors and of products are very different, and then 
only over comparatively wide temperature ranges. In other cases, 
such as the combustions of organic liquids, though the several specific 
heats are widely variable, the average specific heats of factors and 
products are not very different; so that the heat evolved, even over 
wide ranges of temperature, remains fairly constant. In such cases, 
moreover, the temperature coefficients of different reactions are similar, 
so that from the data supplied by measurements of these energy 
changes the comparative heats of formation of many organic com- 
pounds may be deduced with considerable accuracy. 
The variation between the specific heats of the substances involved 
^ The statement is usually formulated (lo): 
K,-K = ^^-~^ (I) 
Where is the initial, and K the final heat capacity of the'system; where t is the 
temperature change; and where Ur-^-t— Z7r represents the'change in the total energy 
within this interval. For small temperature differences the formula may be written 
