150 CHEMICAL TRANSFORMATIONS IN 



4. The most general form of the equation is where a number 

 of substances, A, B, C, etc., react with one another to form a 

 number of other substances, A', B', C', etc., and where the number 

 of molecules of each substance entering into reaction varies. 



Let the chemical equation be represented by 



aA. + 6B + cC + etc. 7 a'A' + 6'B' + c'C' + etc., 



in which the small letters represent the numbers of molecules of each 

 substance respectively entering into reaction. Then the expression 

 for the change in volume energy becomes 



CP P , P , P. P 



a' log p A +6' log p B +c' log p c +etc. -(a log p +b log p B 



p -i 



+ c log p + etc.) . 

 M) 



This expression can be written 



Pff.P;:.Pg'.etC. p [a+&+c+etc.-(a'-f6'+c'+etc.)l 

 .It _L lOg p a pj p c 



For equilibrium, as before, this expression is equal to C, the energy 

 evolved when a grm. molecule of each substance changes from the 

 left-hand side of the equation to the right, and hence 



PJ.PJ.PJ.etC. p [-*+ 6+ c+etc. -('+&'+<:'+ etc.) I t 



or 



(> 



Pff.PS/.P*,.etc._p [a'+b'-}c'+etc.-(a+b+c+ctc.)] m e mf. 



P^.P 6 B .P7etc.~ 



Now the right-hand side is a constant, so the general equation of 

 equilibrium becomes 



p&', i 



~'- = constant. 



The results which can be derived from the types of reaction that 

 we have considered may now be discussed. Writing K for the constant, 

 we have the following results : 



I. Where a single substance A undergoes molecular rearrange- 

 ment to form a single substance B : 



