148 CHEMICAL TRANSFORMATIONS IN 



is equilibrium, and the equation of equilibrium is 

 ET log ^i" = C = const, i 



* 4 -* B 



At any other point in the reaction the heat of reaction for a grm. 

 molecule changing form at the given pressures is given by the equation 



or 



/ 77 7) P P 



HT?T l'\nr T rc-l'v -i x c' X 

 = K1 I log - -log p-p 



\ PA-PK r A r 



or 



If at the beginning ol the reaction A and B are present in equal 

 molecular concentrations, then since an equal number of molecules of 

 each always disappear in the reaction, and an equal number of C and 

 D appear as the result, at every stage P A = P B and P C = P D . Hence 



P 2 P 



the equation of equilibrium simplifies to C = RT log p A 2 = 2RT log p A , 



*0 -* c 



P 



and that for the heat of reaction to H=C~2RT log p A , or H = 2RT 



3. Take next a type of reaction which is one of the com- 

 monest, and which is almost universally met in the problems 

 of biological chemistry namely, the type in which a single com- 

 pound on one side of the equation breaks up into two or more on 

 the other side, or a reaction in which, although two substances 

 react on each side of the equation, one of them is identical with 

 the solvent, so that it causes no change in volume energy when it 

 appears or disappears in the reaction, such a reaction occurring 

 in aqueous solution, for example, as 



CiaHaAi + H 2 ^ C C H 12 6 + C 6 H 12 0, 

 (Maltose) (Dextrose) (Dextrose) 



Using the same notation as before, let P A be the osmotic pressure 

 at any stage in the reaction of the single substance which undergoes 

 change in osmotic pressure on the left-hand side of the equation, and 



P .P 



C KT 



. 



1 As before, this quotation may be put in the form T> C p- = e KT , which if 



-LA -LB 



P A =P B , and P c =P D , may be further simplified to ^ =e 2KT . 



