326 ORGANISATION IN SPACE AND TIME 



The kinetics of processes occurring within open systems 

 are very complicated and pecuHar to them. We shall try to 

 explain the kinetic peculiarities of the chemical reactions in 

 open systems by analogy with the simplest hydrodynamic 

 model of stationary systems. A vessel with a liquid flowing 

 through it may serve as such a model.'' This is represented 

 diagrammatically in Fig. 3 1 . 



The vessel S in which the liquid stands at a constant level 

 represents the source of substances entering the system (the 

 external medium). The vessel Z is a sink (this also represents 

 the external medium into which the system discharges the 

 products of the reactions which have occurred within it). 

 The open system itself is represented by the vessels A and B 

 which are connected with the ' external medium ' by means 

 of the taps Ko and Kz which represent the diffusion constants 

 of substances into and out of the system. The stationary state 

 of the system is attained when the water is at particular 

 levels in vessels A and B, which correspond to stationary 

 concentrations of the substances taking part in reactions in 

 the chemical open system. Tap K regulates the flow of water 

 from A to B and represents a constant rate of the reaction 

 with which we are concerned, A -^ B. There is also shown 

 a kymograph which records, by means of a float, the level 

 of the water in vessel B. 



When the flow of water through the system has been 

 established, this level will remain constant like the static 

 level of water in an ordinary bucket. In our system, however, 

 there is a continual dissipation of energy due to the flow 

 of the water. This is what maintains a constant level in 

 vessel B. 



To make it easier to follow the analogy between the hydro- 

 dynamic model and the chemical reaction in an open system 

 we may give the following diagram 



! I 



I I 



Ko I Ky I Kz 



S — > A ^i^ B — > Z 

 I K, I 

 I I 



