VELOCITY OF REACTIONS 



centration of one substance was changed. Such 

 reactions are called Reactions of the First Order, or 

 Monomolecular Reactions. Most of the reactions 

 which take place in living cells seem to belong 

 to this order. The determination of the substance 

 still remaining can be made in different ways. 

 Very often polarimetric control of the liquid in 

 which the reaction takes place allows of a very 

 exact conclusion on the rate at which the substance 

 disappears. The refraction of light, or even a 

 change in colour, can be used as a reagent of the 

 chemical process. 



In other cases the law of the reaction is a different 

 one. We find that the reaction velocity is not 

 directly proportional to the quantity of the 

 reacting substance, but proportional to the square 

 of this quantity. In all such cases, two substances 

 are simultaneously changed in their concentration. 

 Such a process takes place in the decomposition of 

 esters, the compounds of organic acids and 

 alcohols, under the influence of an alkali. There 

 the concentration of the compound is continuously 

 diminishing. But, on the other hand, the con- 

 centration of the alkali, which is used up in the 

 formation of the alkali salt of the organic acid, also 

 decreases. So it is, for instance, in the reaction 

 between sodium hydroxide and ethyl acetate : 



CH 8 -C 2 H 6 OOC+N*OH = 

 N0OOC-CH 3 +C 2 H 5 OH. 



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