Reaction before Complete Equilibrium. 471 



The present conceptions of the velocity of chemical reaction 

 in heterogeneous systems, and of chemical equilibrium in 

 heterogeneous systems, can thus be summed up in the follow- 

 ing few general statements : 



The active mass of a solid (or liquid) substance is, before 

 and at the equilibrium constant (K), independent of the 

 quantities of the solid (or liquid) substance. The velocity with 

 which one or more gases (or substances in solution) combine to 

 form a solid substance is K f p 1 , " , 'p/"*' . . ., where /?/, pj . . . are 

 the concentrations of the gaseous substances (or of the substances 

 in solution) at the time r, and »/ 3 nj are the number of molecules 

 with which each gaseous substance takes part in the reaction; 

 this velocity is independent of the quantity of the solid. When 

 both opposite reactions become equal, a dynamic equilibrium 

 is present. 



In this way we are able to explain or interpret the experi- 

 mental data observed for chemical equilibrium in heterogeneous 

 systems. But on the other hand there are almost no experi- 

 mental observations concerning the velocity of reactions in 

 heterogeneous systems, and we are therefore necessarily com- 

 pelled to be very cautious in drawing conclusions from facts 

 observed at equilibrium for the velocity of reaction in the 

 system before equilibrium has taken place ; the more so as the 

 above is not the only interpretation possible. Another, which is 

 more in conformity with the facts concerning the velocity of 

 reaction as far as they are known to the chemist at present, 

 may be formulated thus : The active mass of a solid (or liquid) 

 substance is at the time r before and at the equilibrium directly 

 proportional to its surface St. The velocity with which one or 

 more gases (or substances in solution) combine to form a solid 

 (or liquid) substance at the time r is WpJ n 'pJ n ^ . 2 T , i. e., is at 

 the time r a function of their concentrations as well as of their 

 surface of contact with the solid, which is also 2 r . The total 

 velocity before equilibrium is 



~ =k . %z kvv • s T = s{k z kw-') 



At equilibrium 



(^)=2t(k -KV«V S2 ') =o=KZK'p^'p 2 ^'. 



These general statements explain just as well as those 

 given before all the facts observed at equilibrium of hetero- 

 geneous systems, and give at the same time a more correct 

 form for the equations for the velocity of reaction. It is well 

 known that when an acid solution, for example, is acting upon 



