CHEMICAL THEORY OF SOLUTIONS. PAßT I. 31 



Z" = Vj /^i + y. /-'s + 



is of course valid for any temperature. On differentiating with 

 respect to T we get : 



where K has the meaning defined by equation (14), but is no 

 longer constant as the temperature is considered variable. From 

 the definition of Z", z^, Zo, it follows: 



^ = -S", ^=-S,, 4|-=-&, e.c. 



where S" is the molecular entropy of the solid compound 



©1^ ©2v„ J aiicl Si, Ä, are the molecular entropies of 



the components in the liquid state. We have therefore, 



l^rj^UnK ^ ^^^5,^ ^^^^5.^^ -S"-lilnK. 



But as —RTlnK'i^ nothing but the maximum work obtainable 

 by mixing the liquid components in the proportion necessary 

 for the formation of one mol of the compound, we have the 

 followino; relation : 



'0 



V, S, + v,S.+ - S"-It In K = ^, 



where Q is the molecular heat of fusion of the comj)ound. The 

 foregoing differential equation reduces therefore to : 



îilnK _ Q 

 dT liT-' ^ ^ 



