LAWS OF ELECTROLYTIC DISSOCIATION 5 



ions has progressed to unequal extents. This reaction occurs with 

 such prodigious velocity that we can have no conception of the 

 intermediate stages; the cause lies in the fact that the two blood 

 samples have actually a different chemical composition. The first 

 chapter of this book deals with the laws of this true ionic equilib- 

 rium, and its basis is, therefore, the law of mass action. 

 The meaning of the law of mass action is as follows: 

 1. A simple special case: When any molecular species A decom- 

 poses (''dissociates") into two molecular species Bi and B2, then the 

 equihbrium, i.e., the apparent standstill of the reaction, is reached 

 as soon as 



[A] 



[Bi] . [B,] 



= k 



The brackets denote the molar concentrations of the inclosed sub- 

 stances. The constant k depends upon the nature of the reaction 

 and the temperature. It is called the affinity constant of the reac- 

 tion. Its reciprocal value 



[Bil [B2] 



lA] 



is called the dissociation constant of the substance A. 



2. General case. When 1 molecule Ai + 1 molecule A2 + 

 .... are transformed into 1 molecule Bi + 1 molecule B2 + 

 . . . . , equilibrium is reached when 



[Ai] • [A,] . ■ . . ^ 

 [Bi] . [B,].... 



When two or more of the reacting molecular species are identical, 

 the rule is applied in the same way as above; as for instance in the 

 oxy-hydrogen gas reaction: 



1 mol. H2 + 1 mol. H2 + 1 mol. Oo ^ 1 mol. H2O + 1 mol. H5O 

 hydrogen oxygen water vapor 



equilibrium is attained when 



IH2] • [H2] . IO2] 



[H2O] . [H2O] 



= k 



