384 KEYES ART. J 



vertibility of the simple and complex molecules cannot be 

 arrested. The apparent heat capacity of the gas mixture will 

 therefore consist of the sum of the heat capacities of quantities of 

 the NO2 and N2O4 molecules dependent on the temperature and 

 pressure and on the heat absorbed in the shift of the molecular 

 species while the mixture is being changed in temperature. An 

 exact knowledge of the ratio of the number of mols of NO2 and 

 N2O4 as a function of temperature and pressure would of course 

 enable such apparent heat capacities to be operated upon with a 

 view to extracting the heat capacities of the separate molecular 

 species, but it is quite impossible to evaluate the terms of 

 equation (114) [309], for example, without the heat capacity 

 data. It might be supposed that (114) [309] could be evalu- 

 ated omitting the heat capacity terms as a first approximation, 

 and that with such a provisional relation between the amounts 

 of NO2 to N2O4 as a function of p and t one could treat the 

 apparent heat capacity data. The provisional values of the 

 heat capacities could then be used to secure a second approxi- 

 mation of the reaction equation, and this in turn would permit a 

 further refinement in computing the true heat capacities. But 

 this tedious process could not lead to an exact result since 

 in the treatment the perfect gas laws would be involved. 

 Of course, sufficiently precise measurements of the actual 

 density of the mixture would conceivably permit a semi- 

 empirical formulation with (114) [309] as a basis, provided the 

 composition of the mixture could be exactly determined. This 

 is, however, a matter of the greatest difficulty because of the 

 great reaction mobility so that, generally considered, the exact 

 interpretation of density data for mutually convertible com- 

 ponents in terms of the numbers of the reacting molecules, the 

 pressure and the temperature, must be admitted to be sur- 

 rounded with difficulties. 



We proceed with the application of equation (114) [309] by 

 omitting all the heat capacity terms and writing for ZviEi 



^viH\ — "EviR 



AE, and for the symbol I, giving 



K 



l«S^r^= - ^+^- (118) [309] 



Kt x^^Q lit 



