THERMODYNAMICS AND KINETICS ^29 



may serve as an example of the course of an enzymic reaction 

 showing the characteristic features of reactions in open 

 systems: a change in the stationary state, the dynamic 

 stabilisation inherent in the system, and the transition from 

 one stationary state to another through an extreme state 

 (through a minimum). Thus, for every open system there 

 must be an unlimited number of stationary states in which 

 any change, even of only one of the parameters of the system, 

 will, in principle, necessarily lead to the establishment of a 

 new stationary state. 



If several reactions are taking place within the system 

 instead of only one, and if these follow one another in a 

 longer or shorter chain of transformations or are, in general, 

 associated with one another in time, then the equation for 

 stationary concentrations in open systems becomes far more 

 complicated. For direct, unbranched, chains of reactions, for 

 example, it may be represented as follows : 



Kq\ Ki Ki K3 K4 ^n—1 '-^z 



S > A ^ B ^ C , . D ,^ — ,^ N > Z 



The chains of chemical reactions taking place within open 

 systems may, however, branch, e.g. : 



S->A^B^C^D^ ^ N -> z 



1L t •• 



X ^ ^ Y 



This may lead to the formation of a complicated network 

 of reactions with many branches and internal cycles. It may 

 be compared, in some respects, to a railway network on which 

 a large number of trains are moving in various directions at 

 various speeds. On the basis of his own profound kinetic 

 analysis of these phenomena C. N. Hinshelwood^* concluded 

 that in networks of chemical reactions of this sort the limiting 

 states are not always determined by the slowest individual 

 reaction forming a separate link of the chain but depend 

 on the relationships of a whole series of reaction-velocity 

 constants. In fact, in a complicated network of reactions, 

 the transition between two chemical states may occur, not 



