; 



86 KINETICS OF CHEMILUMINESCENCE 



for the temperature dependence of </> which fits the experimental data 

 reasonably well. 



An alternative explanation for the variation in the efficiency of light 

 production is that there is a change in the fraction of molecules passing 

 along the reaction route favorable to light production. Inasmuch as 

 there is only a relatively small change in the quantity of light emitted 

 as the temperature is changed, the error in assigning the entire effect 

 to changes in <f) will be small in the case yet to be considered. 



Although the temperature control was not too good in these experi- 

 ments, it was possible to obtain an approximation of the rate as a 

 function of temperature by noting the time for the intensity to drop to 

 various fractions of the initial intensity. That is, 



_ ^ = k'[X][Y] (13) 



where Y is the concentration of the species that remains essentially 

 constant, which in this case is the ferricyanide, and X is the concen- 

 tration of luminol. Equation 13 can be rewritten as 



at 



The quantity d In X/dt is equal to d In I/dt where I is the intensity 

 of the light in as far as </> is independent of concentrations. Values for 

 d In I/dt are given in Table I. 



If the standard state is taken as 1 mole per Hter, the values for 

 d In I/dt divided by the concentration of the ferricyanide will give 

 values for fc". These values are also tabulated in Table I. 



The rate equation for k' is 



k' = .^e-AZ/i/flreAsV/s (9) 



h 



If this is divided through by T and the logarithm is taken, the equa- 

 tion becomes 



1,^.1„,^-_A^ + ^ (15) 



^'' T h RT ^ R 



As can be seen, a plot of In k'/T versus l/T should give a straight line 



