CHAPTER III 

 REACTIONS IN HETEROGENEOUS SYSTEMS 



THE outstanding feature of heterogeneous mixtures is 

 that there are surfaces separating the various homo- 

 geneous substances or phases. These surfaces show 

 peculiar characteristics which are termed surface tension 

 phenomena. They are best exemplified by liquids and owing 

 to their influence on the ascent of liquids in capillary tubes 

 they are often spoken of as capillary phenomena. We must 

 examine the influence of these surface phenomena and compare 

 them with the equilibrium conditions in the various phases 

 separated by the surfaces. 



DISTRIBUTION BETWEEN Two PHASES 



The solubility of a gas is generally proportional to the 

 concentration (pressure) of the gas. This is known as Henry's 

 Law* and is applicable only when the gas is in the same 

 molecular condition in the solution and in the space above 

 the liquid. 



If the dissolved gas forms double molecules the concentration 

 in the solution is proportional to the square root of the pressure, 

 and if the gas is combined with anything in the solution the 

 total amount dissolved may not bear any simple relation to 

 the gas pressure above the solution. That is a departure from 

 Henry's Law indicates that the gas is not dissolved in the same 

 molecular condition^in which it occurs in the gas phase. 



The distribution "of substances between* various phases 

 follows the same law, hence any departure from direct pro- 

 portionality between the concentrations in the various phases 

 requires investigation to discover the cause of the discrepancy. 



SURFACE TENSION 



The cause of surface tension is the attraction of the molecules 

 in the bulk of the liquid on the molecules in the surface. 

 These surface molecules are attracted on one side only as 



* W. Henry, Phil. Trans., 1803, p. 29. 

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