671 



which relation remains valid, follows for T =: 



if 5 represents the entropy. 



If we now calculate the change of entropy which occurs on mixing 

 two ideal gases (i.e. gases, in whose equation of state no members 

 occur which depend on the volume and the mutual attraction of 

 the molecules) by supposing this mixing to take place in a reversible 

 way at constant temperature, it follows from the last mentioned 

 relation that at the absolute zero the entropy change on mixing is 

 equal to 0. 



§ 2. The theorem indicated in the former § may be further 

 elucidated by means of relations for the equation of state of an 

 ideal gas which I deduced in Suppl. N". 30? (May '13). It seemed, 

 however, desirable to me as the foundations of the considerations 

 of § 1 not to make more assumptions than are strictly necessary. 

 For against several of the special assumptions of Suppl. N°. 30a, 

 particularly against the use of Debije's method in the way as is 

 done there for an ideal gas, more or less serious objections can be 

 made. All the same the deviations from the equipartition laws, which 

 will become apparent in the equation of state of an ideal monatomic 

 gas, are presumably given rightly in a qualitative sense by those 

 relations. Further it seems to me that one may expect with some 

 contidence that the order of magnitude of those deviations will agree 

 with that of the deviations given by the relations mentioned. For 

 this reason it seems to me to be not quite superfluous to indicate 

 here what may be derived for the entropy of an ideal mixture from 

 those relations. 



a. From equation (1) of Suppl. W. 30a with (2), (3), and (5) of 

 that paper follows for a one-component gas, if molecular rotations 

 and intramolecular motions are left out of account ^), 



/(v 



f "max J \T !^ \ )\ 



(6) 



,kT_\ 



With 





') This expression was already given by H. TEfROUK, Pliysik. Z.S. 14 (1918), 

 p. 212. 



43* 



