Competing Mechanisms and the Principle of Detailed Balance

18 For a fixed total enzyme concentration, a certain enzymatically catalyzed reaction has an initial rate of 0.0015 mol min for an initial reactant concentration of 0.100 mol and an initial rate of 

For any reaction that proceeds by two competing mechanisms, the principle of detailed-balance governs the rate constants for the two mechanisms Different mechanisms for the same reaction must give the same value of the equilibrium constant at the same temperature. Another statement is At equilibrium, each mechanism must separately be at equilibrium, with canceling forward and reverse rates. Because of this principle, a catalyst cannot change the equilibrium constant for a reaction, and a catalyst must catalyze the reverse reaction if it catalyzes the forward reaction. 

Assume that a gaseous system containing H2, I2, and HI has come to equilibrium. Consider two mechanisms for the reaction of H2 and I2 (1) the mechanism of Eq. (12.5-15) with inclusion of a reverse reaction in step 2, and (2) the elementary mechanism  

13 Chemical Reaction Mechanisms II Catalysis and Miscellaneous Topics 

Since both equilibrium constants refer to the same reaction, they must be equal  

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Section 13.2 Competing Mechanisms and the Principle of Detailed Balance... 

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