THERMODYNAMICS AND KINETICS 333 



As we have shown above, at a particular stage in the history 

 of the Earth, diverse organic substances were formed and 

 reacted chemically with one another in many different ways. 

 The participation of free radicals, which were formed as a 

 result of the effects of ultraviolet radiations, electric discharges 

 and radioactive radiations, still further increased the number 

 of possible reactions. Over a long period it is probable that 

 almost all the possible chemical reactions between the sub- 

 stances present actually took place to a greater or less extent. 

 However, in the general disorderly association of all con- 

 ceivable chemical reactions of those times, a single chemical 

 reaction probably predominated at any particular place and 

 others in other places. This was essentially due to the fact 

 that the transformation of any substance entering into a 

 reaction preferentially followed the chemical course which 

 assured the greatest speed of reaction under the given circum- 

 stances. 



According to the theory of chemical kinetics, if the differ- 

 ence in free energy, Af, is the same for all the reactions, 

 the transformation of the bulk of a given substance will 

 follow the course of reaction along which it can proceed most 

 quickly. The attainment of the greatest speed for a given 

 reaction depends, in its turn, both on the chemical nature 

 of the reacting substances and on the local conditions of the 

 medium, temperature, pressure, and particularly the pres- 

 ence of appropriate catalysts, especially when such a catalyst 

 specifically accelerates only one of all the possible reactions. 



This may be illustrated by the following elementary 

 scheme. Let us suppose that we have any organic substance 

 A, which can be transformed into substances B, C, D, etc. 

 In our scheme the rates of these reactions are represented by 

 the vectors, the length of ^vhich indicates the rate of any 

 reaction. 



C 



D ^ A > B 



In this diagram we see that the rate of the reaction A -> B is 

 seven times that of the reaction A -^ D which, in its turn. 



