476 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Chatelier as far as heat is concerned. In order to trace this evident 

 necessity, one must assume a somewhat puzzling inverted attitude. The 

 pressures indicated by the formula define a condition of equilibrium, not 

 a condition of action. It is clear, then, that a small pressure in the 

 numerator of the logarithmic expression means a great tendency towards 

 the denominator. That is, a growing denominator means an increasing 

 tendency to change from factors to products. But the logarithms in the 

 denominator take the minus sign, or the sign of Q, which represents 

 heat absorbed. Hence a reaction which absorbs heat evidently must be 

 pushed farther by increasing temperature. 



The inverted attitude just mentioned may be easily remedied by con- 

 sidering carefully the nature of the quantities involved. We have seen 

 that the expression 



P2'^P 2 = • • • 



the familiar " mass-law " expression for equilibrium expressed in terms 

 of pressure, seems to represent the resultant reacting tendency of a given 

 reaction at constant temperature ; because it is this quantity which is 

 concerned with the theorem of Maupertuis. When concentrations are 

 used, it is difficult to imagine any physical meaning in this equilibrium 

 ratio ; but when the expression is conceived of in terms of pressure, 

 we may look upon k as an opposing tendency which has been balanced 

 by the ratio of the pressures observed. That is, we may call k the 

 "reaction tendency." This means not merely pressure, but work ; be- 

 cause the expression R T \ ~ from which it was originally derived 



means work. It represents then the variable factors in the " driving 

 enerfry " of the reaction. 



AVe may conceive of this reaction tendency as consisting of a number of 

 individual reacting tendencies, one for each substance. But the pres- 

 sures in the pressure-equilibrium ratio do not directly represent the 

 individual reacting tendencies of the substances represented. They are 

 only the pressures which remain in equilibrium when all the reacting 

 forces have been balanced. When under the circumstances a given 

 individual pressure is small, we must ascribe to that substance a great 

 reacting tendency, and vice versa. Thus it seems to me probable that 

 each of these pressures must have a term in the function k which corre- 

 sponds to its tendency to react, and this individual tendency we shall 

 call In 2, — a term which will be in the numerator when the correspond- 



