258 THE REALITIES OF MODERN SCIENCE 



phases. This position is determined in the present case 

 by the temperature. Increasing the temperature means 

 shifting the equilibrium in a direction corresponding 

 to increased vapor. 



In an electrolyte at a given temperature there is 

 equilibrium between the rate at which molecules are 

 dissociating and that at which they are recombining 

 due to collisions. Let us represent the molecule by AC, 

 where A stands for anion and C for cation. There are 

 taking place in the solution two reactions, AC >-A + C, 

 and A-fC *-AC or AC-* A-j-C, that is, the dissocia- 

 tion of molecules and the recombination of ions. Let 

 the rates be expressed in molecules per second as 

 k d and fc, respectively. When the solute is added 

 to the solvent, k c is zero and k d is a maximum. As 

 ionization occurs the number of normal molecules 

 decreases and hence kd, the number ionized per second, 

 also decreases. On the other hand k c increases. When 

 the two rates become equal equilibrium l results. 

 Thereafter dissociation and recombination occur, but 

 the average number of dissociated molecules remains 

 constant unless we change some of the conditions, 

 e.g. the temperature or the concentration. 



The rate of recombination will obviously depend 

 upon the frequency of collision of the ions which are 

 necessary to form a molecule, and hence upon the 

 concentration of each of these ions. Thus in the present 



1 In the case of a solution the equilibrium is reached very quickly 

 provided that the solute is either in a liquid form or finely powdered. 

 If the solute is in the solid form it is evident that but few of its mole- 

 cules are accessible for reaction with those of the solvent, and hence 

 that the value of kd will be limited by the supply of dissolved 

 molecules. 



