Rate Expressions and the Method of Flooding

Consider all of the conceivable rate equations that have the form 

The solutions of these equations under a particular set of constraints can be worked out. But that approach is not profitable, since simplifying conditions are usually chosen. Thus, at least some of the species that affect the rate would be added at a relatively high concentration or buffered. 

If concentrations are known to —1-2 percent, a minimum of 10-fold excess over the stoichiometric concentration is required to evaluate k to within a few percent. The origins of error have been discussed.14,15 If the rate law is v = fc[A][B], with [B]o = 10[AJo, [B1 decreases during the run to 0.90[A]o. The data analysis provides k (the pseudo-first-order rate constant). To obtain k, one divides k by [B]av- If data were collected over the complete course of the reaction, 

Better yet, a least-squares analysis of k versus [B]av is carried out. The order with respect to [A], the limiting reagent, is established from the fit of the data to a chosen rate law. Experiments over a range of [A]o are a preferable way to show the order in LA], At constant [B], will be the same regardless of [A]o if the rate is first-order with respect to [A], 

The order in [B] is determined by varying [B]o- It is best to use a wide concentration range, to be certain of the correct functional form. The case v = fc[A][B] is easily recognized, since the plot of k versus [B] is a straight line that passes through the origin. 

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