THERMODYNAMICS AND KINETICS 



325 



librium there is, as a rule, no change m free energy, whereas 

 in the stationary state the free energy enters and leaves the 

 system at the same constant rate. 



Thus, the stationary state is kept constant, not because the 

 free energy is minimal (as is the case in thermodynamic 

 equilibrium) but because the system is continually receiving 

 free energy from outside in amounts which compensate for 

 its decrease within the system ; it is ' fed ' with free energy 

 at the expense of the environment. 



iL 



. n 



Pi. 



K rwOORAPH 



WATER MODEL OF 

 A STEADY STATE SYSTEM 



Fig. 31. Water model of the Fig. 32. Records made with the water 



simplest steady state system. model of a steady state system. 



A. Change of k to new level with 

 k <k . B. Same with k > k . C. 



o z o z 



Single and repetitive brief changes of 

 k with A- <:k . D. Same with k > k . 



o z o z 



Reproduced by permission from originals of Figs. 8 and 

 9, Alan C. Burton, /. cell. comp. Physiol., /./, 344. 



Similarly the entropy of a closed system in equilibrium is 

 at a maximum, whereas, in an open system in the stationary 

 state, it is kept constant but not maximal. The chemical 

 thermodynamic theory of irreversible processes occurring in 

 open systems has so far only covered small deviations from 

 thermodynamic equilibrium. From the results of H. Eyring 

 and others^" it would seem that it is only applicable where 

 Az = about 02 kcal/mole. However, within these limits 

 thermodynamics has established that, in general, there are 

 linear relationships between the changes in properties of the 

 system (e.g. chemical transformations or the diffusion of 

 substances) and the strength of the forces acting on it (the 

 giadients of free energy, concentration, temperature, etc.) for 

 a number of simultaneous processes. 



