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XXI. The Influence oj Temperature on Homogeneous Gas 

 Reactions. By George W. Todd, D.Sc. {Birm.), B.A. 

 {Cantab.), and S. P. Owen, B.Sc. {Wales) *. 



IT is well known that a small rise in temperature generally 

 causes a big increase in the velocity of a chemical re- 

 action — a rise of 10° C. often doubles or even trebles the 

 velocity. On the kinetic theory of gases the frequency with 

 which the molecules collide is proportional to the absolute 

 temperature, so that a rise of 10° C. in normal regions of 

 temperature would only result in increasing the frequency 

 of collision by two per cent. For this reason the kinetic 

 theory as a means of explaining the effect of temperature on 

 reaction velocity and on chemical equilibrium has been left 

 severely alone and artificial assumptions such as the "active " 

 and " passive " molecules of Arrhenius have been brought 

 forward. 



Many years ago Boltzmann (Wied. Ann. xxii. p. 64) 

 pointed out that a kinetic treatment of gaseous equilibrium 

 ought to give better results than a thermodynamic treat- 

 ment. As yet no results of practical importance have been 

 obtained in this way. 



The majority of the molecules in a gas are moving with a 

 velocity not far removed from the average, but whatever the 

 temperature there are at every instant a very few molecules 

 practically motionless and a very few with extremely high 

 velocities. Now it is quite certain that in a chemical re- 

 action only a small proportion of the molecules are in the 

 condition for combining, at any instant of time. We shall 

 therefore assume that a gas molecule can never react with 

 another gas molecule unless its energy (we shall take kinetic 

 energy in what follows) surpasses a definite minimum. 



According to Maxwell's theorem on the distribution of 

 velocities the number of molecules in 1 c.c. with velocities 

 between c and c+dc is 



where N = number of molecules per cc, 



R = gas constant, 

 m = mass of a gas molecule, 

 = absolute temperature. 



* Communicated by the Authors. 



