172 VELOCITY OF REACTION, AND 



tion, then removing the catalyst and excess products of activity, 

 and replacing the catalyst again, energy could be continually 

 manufactured from nothing, or working in the opposite direction 

 energy could be destroyed; both which results are obviously con- 

 trary to the law of conservation of energy. 



To this reasoning the following objections may be taken: 



1. The assumption is wrong that because the catalyst is not 

 permanently altered in the process it cannot therefore take up or 

 give out energy to the system, because it excludes (a) the possibility 

 of the catalyst operating upon external energy, which is done, for 

 example, by the chlorophyll-bearing cell; (6) the possibility of the 

 catalyst using part of the chemical energy of the system, to run 

 another reaction in which energy is absorbed, as is done by all 

 living cells. 



2. Even for catalysts in the restricted sense, there is nothing 

 in the reasoning to show that the catalyst cannot take up and give 

 out energy in a vibratile fashion, so that as a net result its own 

 condition and amount of energy is unaltered, and its condition at 

 the end is the same as at the beginning, and yet by this means it 

 can induce a reaction which would not occur at all in its absence. 

 For example, an electro-motor is not altered at the end of a period 

 of running from what it was at the beginning, but by intermedi- 

 ately taking up an amount of energy it is capable of converting a 

 large amount of electrical energy into mechanical energy which 

 would never have occurred if it had not been in the electric circuit. 

 So when a chemical reaction is absolutely stationary on account 

 of opposed molecular attractions present in the molecule having 

 a tendency to react, the enzyme, by imparting momentarily a small 

 amount of energy to the molecule, may overcome the molecular 

 attractions, and in the break-up of the molecule may receive back 

 all the energy previously given out, so as to remain unchanged in 

 the process. 



Finally, as has been pointed out above, the presence of the 

 catalyst may not cause the reaction to proceed completely to the 

 equilibrium point, because as the reaction proceeds, and the con- 

 centration of the substance reacting changes, the potential tendency 

 backing the action of the catalyst may fall to such a level that the 

 energy in the first stage which the catalyst is capable of yielding is 

 insufficient to cause the cleavage to occur. Hence the reaction may 

 cease at a different point with different catalysts. 



