28 CHEMICAL TRANSFORMATIONS 



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

 equilibrium becomes 



PI;.P# P<C.&C. 



- -- -= 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 resiilts : 



I. Where a single substance A undergoes molecular rearrange- 

 ment to form a single substance B : 



PB Si- 



P-= :K ' ] PB = K:PA ' 



If the chemical energy of transference from substance A to sub- 

 stance B is zero, the constant becomes unity and the equation 

 is P B = P A . This condition is probably attained with stereo-isomers, 

 and hence when the two isomers are formed in any reaction they 

 are turned out in the condition of equilibrium, that is, in equal 

 quantities, and we get, as in the case of the synthetically prepared 

 sugars, the indifferent compound consisting of an equimolecular 

 mixture of the two isomeric bodies. 



II. Where two substances, A and B. interact to form two 

 others, C and D : 



c_ 



that is, the product of the osmotic pressures of the one pair of 

 substances is proportional to the product of the osmotic pressures 

 of the other pair of substances. 



If the substances A and B at the commencement are in equi- 

 molecular concentration, then P A = P B , and since the substances 

 C and D are then also formed in equimolecular concentration 

 also P c = P D , and hence the equation for equilibrium can obviously 

 be simplified to P (C or D) = K . P (A or B) . That is, the osmotic 

 pressure of the substances formed always bear the same ratio to 

 the osmotic pressure of the substances from which they are formed 

 when the equilibrium point is reached. 



It follows that for reactions of the type I., and for those of 

 II. when the substances are present in the proper equimolecular 



