THERMODYNAMICS AND KINETICS 327 



Here the dotted lines represent the boundaries of the open 

 system, such as the cell wall or the surface film of a coacervate 

 drop. S and Z represent the external medium, Ko and Kz 

 the velocity constants for diffusion or penetration of the 

 membrane, K^ and K^ the velocity constants for the chemical 

 reaction A^=^B taking place within the open system. In 

 the hydrodynamic model if we alter the setting of the taps 

 Ko and Kz (which would be the equivalent of changing the 

 rate of diffusion in the chemical analogy) or turn tap K 

 (which corresponds to a change in the rate of reaction), then 

 a new level will be established in vessel B, i.e. a new station- 

 ary state will be set up. Thus it is possible to establish an 

 infinite number of stationary states in an open system, 

 depending, particularly, on changes in the rate of the reaction 

 which is occurring within the system. 



It is well known from the classical kinetics of closed systems 

 that the introduction of a catalyst into a system will alter 

 the speed with which it reaches equilibrium, but does not 

 affect the position of the equilibrium because the magnitudes 

 Ky and K2 are changed in such a way that the ratio between 



K 



them remains constant {K =-~). Two ordinary vessels con- 



taining water at different levels and connected with one 

 another by a tap may serve as a hydrodynamic model of such 

 a closed system. The amount which this tap is open will 

 affect the rate at which the fluid level becomes the same in 

 both buckets but will not affect its position. 



In open systems, on the other hand, the introduction of a 

 catalyst will, as we have already seen, change not only the 

 rate of the reaction but also the position of the ' equilibrium ' 

 (the stationary concentrations of the components of the 

 system) as may be shown by purely mathematical means. A 

 very characteristic feature of the establishment of a new 

 stationary state in open systems is that it does not come about 

 directly but through extreme states (through a maximum or 

 minimum). 



Thus, at the beginning it deviates more sharply from the 

 original state and later approaches it again more closely 

 (though not completely) as is shown on the accompanying 



