Homogeneous Reaction Rates as Affected by Concentrations of Reagents

HOMOGENEOUS REACTION RATES AS AFFECTED BY CONCENTRATIONS OF REAGENTS 

The law of mass action, proposed by Guldberg and Waage in papers in 1864,1867, and 1879 (25), postulates that the rate of reaction is proportional to the product of the active masses (now thought of as activities) of reagent molecules. When two or more molecules participate in one reaction, each molecule enters independently, so that, e. g., where the reaction reads  

To simplify the treatment, the difference between the thermodynamic active mass, i. e., the activity, and the stoichiometric concentration will be disregarded here, and only the term concentration will be used. Actually quite wide differences between the two are encountered in dealing with such polar molecules as salts and proteins. 

Furthermore, branched or complex chains of reactions can occur, so that, while an increase in the concentration of one initial reactant will accelerate all of the succeeding reactions more or less equally, a block in the removal of a product will divert the reaction to a parallel chain of reactions. Effects of this type make direct conclusions as to rate of reaction from the reagent concentrations open to careful scrutiny. The connection between cause and result in such systems is far from direct. Nevertheless, if we may disregard mutual effects of molecules on the properties of the system, it is permissible to accept the Guldberg-Waage law of mass action as a basis for studies of reaction, provided qll the details of the reaction are known. 

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