Skill 9.6 Analyzing potential energy versus reaction coordinate diagrams

Skill 9.6 Analyzing potential energy versus reaction coordinate diagrams 

Most reaction mechanisms are multi-step processes involving reaction intermediates. Intermediates are chemicals that are formed during one elementary step and consumed during another, but they are not overall reactants or products. In many cases one elementary reaction in particular is the slowest and determines the overall reaction rate. This slowest reaction in the series is called the rate-limiting step or rate determining step. 

The first elementary reaction is very slow compared to the second. Determine the rate law for the overall reaction if NO2 and CO are both present in sufficient quantity for the reaction to occur. Also name all reaction intermediates. 

Solution The first step will be rate limiting because it is slower. In other words, almost as soon as NO3 is available, it reacts with CO. so the rate-limiting step is the formation of NO3. The first step is bimolecular. Therefore, the rate law for 

NO3 is formed during the first step and consumed during the second. NO3 is the only reaction intermediate because it is neither a reactant nor a product of the overall reaction. 

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