CHAPTER IV 



IONIZATION 

 I. IONIZATION OF GASES 



FROM the hypothesis of Avogadro it would be expected 

 that, if a gram-molecule of ammonia and a gram-molecule 

 of ammonium-chlorid vapor were put into chambers of the 

 same size, the pressures exhibited at the same temperature by 

 the two gases would be equal. The latter substance, how- 

 ever, shows a far greater pressure. Now, since the kinetic 

 theory supposes that gas pressure is due to the kinetic 

 energy of its particles, and that the kinetic energy of any 

 particle is dependent only upon the temperature to which it is 

 subjected, we must either reject the theory when we come 

 upon such a case as that just cited, or we must conclude that 

 there are, in the mass of ammonium chlorid, a greater number 

 of particles than in that of ammonia. Several lines of 

 experiment and of reasoning seem to point to this as the 

 true condition of affairs. The number of molecules is the 

 same in both masses of gas, but in the ammonium chlorid 

 it is supposed that many of the molecules split apart into 

 ammonia and hydrochloric-acid ions (NH 3 and HC1), and 

 that, for producing pressure, the ions are as active as would 

 be the same number of molecules. In this way, if all the 

 molecules were dissociated, the pressure should be twice 

 that required by the theory. The ammonium molecule 

 seems not to dissociate at ordinary temperatures. Many 

 gases exhibit the phenomenon just described ; usually ioniza- 

 tion is not nearly complete and the pressure is simply raised 

 above its theoretical value. As the gas becomes more con- 

 centrated, dissociation becomes less and less complete. 



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