214 



SPEEDS OF SOME PROCESSES IN BIOLOGICAL SYSTEMS 



TABLE 8-8. Fluidities (0) poise 1 , or — 



cm /dyne 



sec/ cm 



gases decreases as the temperature is raised (see Chapter 2); but that of all 

 liquids increases with increasing temperature. In liquids the higher the tem- 

 perature the greater the number of particles which have the energy to over- 

 come the internal barriers to flow; or in other words, the higher the tempera- 

 ture the smaller the sticky frictional forces which must be overcome by the 

 gliding laminae, and the faster the flow. The temperature coefficient of 

 fluidity, factored as a specific rate constant, is given in the theory of rates as 



<t> 



V 



In 



-SFt/RT 



V 



h.X 



e ASt/R e -AHt/RT 



where K is the volume of 1 mole of fluid, h is Planck's constant, N is number 

 of molecules per mole, Avogadro's number, and AF X , AS\ and AH X refer 

 to formation of 1 mole of activated complex in the glide plane as it slips from. 

 one position of rest to the next .... The physical analogy between diffusion 

 and flow thus is extended to the algebraic statement of the factors upon 

 which they depend. The two processes can be directly compared in Tables 

 8-7 and 8-8. The experimental values of E* (related to AH 1 ) are usually the 

 same for diffusion and flow (Table 8-3). This indicates the inherent similar- 

 ity of the two processes. Indeed in diffusion the particles move individually at ran- 

 dom from one position of rest to the next. In flow a plane of particles moves as a 

 unit, and no relative motion occurs between members of a plane; adjacent 

 planes glide past each other. The intermolecular forces which oppose dif- 

 fusion are the same as those which oppose laminar flow. That is, the bar- 

 riers to flow are the same, and hence £*'s are the same. The catalysts in 

 this case are called surface-active agents. Washing detergents are good 

 examples. 



The inverse of the fluidity, i.e., 1/0, is called the viscosity, usually ex- 

 pressed by the symbol rj. Hence a high viscosity (cold molasses) means low 



