480 Dr. Meyer Wilderman on the Velocity of 



II. The true meaning of the equations for chemical equilibrium 

 in heterogeneous systems. The laws of chemical velocity of re- 

 action in heterogeneous systems. 



We return to the system given above: NH 4 C1 solid, NH 3 

 gas, HC1 gas. 



At equilibrium no reaction takes place between solid 

 NH 4 0l and gaseous NH 4 01, as is seen from the equation 



* =c(t -t){t-t m + K). 



This means generally : chemical equilibrium in heterogeneous 

 systems depends only upon the reactions which are taking place 

 in the homogeneous parts, since at equilibrium no further 

 reaction occurs between the different parts of the hetero- 

 geneous system. This also explains the fact why " chemical 

 equilibrium in heterogeneous systems is independent of the 

 mass of the solid''': 



*L =c{t -t)(t-U + K) is = 0, when t o —t = 



CLT 



for all values of t — t 0V + K. On the other hand the vapour- 

 pressure of a solid for every temperature is at equilibrium of 

 a definite value, is constant. If the vapour-pressure of the 

 solid ]SIH 4 C1 at equilibrium is p . that ot the gaseous NH 3 or 

 HOI is p, 



f T =K'f-ZK''p o =0; i.e., f=^=K'" 



(observations of Horstman in 1877 for the quite analogous 



case of solid NH 4 SH ^ NH 3 -f SH 2 .) The constant K" is 



therefore not the " active mass of the solid" as assumed, but the 

 ratio of the velocity constants of the two opposite reactions in the 

 homogeneous part. We cannot therefore assume that a phe- 

 nomenon expressed by 



exists where K iv is the active mass of the solid, but we are 

 very well justified in thinking that 



gives the existing relations at equilibrium where p is the 

 pressure of NH 4 01 gas at equilibrium. 



