142 CHEMICAL TRANSFORMATIONS IN 



Hence the state of equilibrium or reaction may be disturbed 

 by addition or removal of energy so as to disturb the potential 

 factors, or by alterations which change the ease of passage from 

 one form to another. 



It is the variation in the potential factor or intensity factor 

 which appeals to our sense organs, and determines the results of 

 all physiological stimulation, and it is for this reason that the 

 potential factor and methods for measuring variations in it 1 were 

 known to mankind long before the recognition of corresponding 

 quantities of energy. 



CHEMICAL ENERGY AND CHEMICAL EQUILIBRIUM. 2 



The energy changes which interest us most in connection with 

 the biological chemistry of the cell are those in which chemical 

 energy plays a part, and accordingly we pass on to the energy con- 

 ditions in a solution. In order to simplify the matter we shall assume 

 at first that there is no catalyst present, and investigate the equations 

 governing energy changes in solution under different conditions in 

 which energy interchanges are possible between the various forms of 

 energy which can react in the solution. That is, we shall leave out 

 of consideration at present the mechanisms by which the energy 

 changes are brought about, which can alter the velocities with which 

 the changes occur, or which, by bringing into play other forms of 

 energy, can alter the conditions of reaction and the equilibrium point. 



The three forms of energy which normally undergo alteration 

 in value when a chemical reaction occurs in solution 3 are the 

 chemical energy, the heat energy, and the osmotic energy. The 

 law of conservation of energy teaches that the algebraic sum of 

 the three alterations must be zero. Or, if C represent chemical 

 energy, 4 H heat energy, 5 and V volume energy, for the change 



1 Such, for example, as the thermometer in connection with heat energy, 

 the manometer in connection with volume energy. 



2 This chapter requires some knowledge of mathematics, but may be 

 omitted, or taken as granted, without disturbing continuity in the reading. 



3 The same holds for gases: the investigation is the same for both con- 

 ditions of matter. 



4 This does not mean heat of reaction, but the total amount of chemical 

 energy sot free or absorbed when a given amount of substance changes form. 



5 The value of H is not the heat of reaction in the usual sense of the term, 

 but the amount of heat energy due to the change of the fixed quantity at the 

 definite osmotic pressures obtaining at a given instant or stage in the reaction. 



