20 CHEMICAL TRANSFORMATIONS 



energy, 1 H heat energy, 2 and V volume energy, for the change 

 of any fixed quantity of matter from one chemical form to the 

 other, we have : 



If attention be paid to change of sign any of these three 

 quantities may be changed from one side of the equation to the 

 other. 



Hence if C represent chemical energy disappearing and given 

 out in the other two forms we have : 



Let us take it that a grm. molecule of the substance changes 

 chemical form, and that the volume of the solution in which such 

 a change occurs is so large that no appreciable change takes place 

 in the osmotic pressures of the two substances in solution. 



Then in the above equation C is the change in chemical energy 

 accompanying a change in chemical constitution from the first 

 form (A) on one side of the chemical equation to the other form (B) 

 on the other side of the chemical equation. As C is dependent 

 only on the change in chemical constitution it is a constant, the 

 value of which is determined by the sum of the values of (1) the 

 heat (H) for the change of a grm. molecule at given concentrations 

 (P 1 and P 2 ) in solution of A into B, the two substances on the two 

 sides of the chemical equation, (2) the change in volume energy 

 due to the conversion of a grm. molecule of A at pressure P X into 

 a grm. molecule of B at pressure P 2 . 



The heat energy produced by the change of a grm. molecule 

 when the substance A has a pressure P X and the substance B a 

 pressure P 2 is a variable quantity dependent upon the values of Pj 

 and P 2 . 



The value of V, the change in volume energy for the change 

 of a grm. molecule of A at osmotic pressure P X into B at pressure 

 P 2 , is also a variable. 



When as the result of a reaction a grm. molecule of a sub- 

 stance comes into solution at a definite pressure, a certain fixed 



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

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



2 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. 



