1046 

 TABLE 4. 



Reaction. 



Reference. 



^f+10 

 k. 



(1) Decomposition of ozone 



Perman and Greaves (Proc. Roy. Soc 

 1908, 80 A, 353) 



BoDENSTEiN and his pupils(Zeit. Phys. Chem. 



1903, 46, 725; 1905, 53, 166; 1907, 60, 1, 

 * 46; 1911, 75, 30; 1912, 80, 148; Zeit. 



Elektrochem. 1905, 11, 373; Festschrift 



W. Nernst, 1912, p. 99. 



Bredigand Teletoff (Zeit. Elektrochem 

 1906, 12, 581 ) 



Jablczynski (Zeit. Phys. Chem. 1908, 64, 748) 



Denham (ibid 1910, 72. 641) 



about 

 1.2 



1.36 



1.40 



1.57 



1.10 



1.18 



1.28 



1.29 

 1.29 



It will be seen at once on glancing at the two foregoing tables 

 that in tlie reactions catalysed by solids (with the exception of blood 

 charcoal) the temperature coefificient is about 1.3 i.e. of tiie same 

 order as that for diffusion; whilst in the case of i-eactions catalysed 

 by colloidal metals and enzymes the temperature coefficient isabout 

 2 i.e. of the same order as that of au ordinary chemical reaction in 

 homogeneous medium. How is this difference to l)e explained? With 

 catalysts, which cause reaction between the substances in rpiestion 

 to take place with practically infinite velocity, the actual rate of 

 reaction will be determined solely by the velocity with which the 

 reacting snbstances diffuse to the surface of the catalyst; whether 

 such a catalyst exists, must of course be determined separately for 

 every case. 



Adsorption is now considered to be an exceedingly rapid process. 

 If the reacting substances were brought to the surface of the catalyst 

 by capillary forces, the temperature coefficient would correspond to 

 'that of the slower process, namely, the chemical change involved. 

 If, on the other hand, the reacting substances are brought to the 

 surface by the slow process of diffusion, then the measured velocity 

 would be that of a diffusion process and the temperature coefficient 

 would be of the oi-der of 1.3, which we have seen in the case when 

 solid catalysts are used. To account for the high temperature coef- 

 ficient in the case of reactions catalysed by colloidal substances and 

 enzymes, one might suppose that the Brownian movement of these 

 particles acted as very efticient stirring in such a way that the 

 diffusion layer was removed as fast as it was formed, with the 



