IN LIVING MATTER 25 



The reaction, as before, can be shown to run exothermally from 



P P 



either end until C = RT log T> ' ,5, at which point energy is neither 



" 



. 



given to nor taken up from the surroundings, hence at this point there 



P P 



is equilibrium, and the equation of equilibrium is RT log T> ' T> p = 



"A PB 



C = const. 1 



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 



Pn . 7?r> Pn . P 



./'A .TB *- A - 1 - B 



or 



D _ 



n <n \ J r 



//A /-'"R *- P -I- T) 



If at the beginning of 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 A 2 P 



the equation of equilibrium simplifies to C = RT log -^ = 2RT log p=* 



p 



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



*c 



H = 2RTAo-^ . ^ 



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

 monest, and that which is almost universally met in the prob- 

 lems of biological chemistry, namely, the type in which a single 

 compound 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 



1 As before, this equation may be put in the form p ' D = e KT t which if 



p 



P A = P B , and P C = P D , may be further simplified to ~~ = e^ T . 



"A. 



