Most reactions that occur at a measurable rate occur as a series of simple steps, each involving a small number of particles, as described in the collision theory. This sequence steps is known as the reaction mechanism. The elementary steps usually cannot be observed directly, thus a theory.
Intermediates are used to split the reaction. The slower step in the sequence is the rate-determining step. This step determines the overall rate of reaction.
The term molecularity is used to an elementary step to indicate the number of reactant particles. Unimolecular reaction is single particle reactant reaction. Bimolecular reaction involves two reactant particles. Anything higher is unrealistic due to collision theory.
16.2.2 Describe the relationship between reaction mechanism, order of reaction and rate-determining step
In the reaction mechanism, the order of reaction is slightly different. Any reaction that happens after the rate-determining step is not included in the overall order of reaction. However, any reaction before the rate-determining step is included.
If there are two of the same molecules used as reactants. In the order of reaction, the concentration has twice the effect hence making it second-order.
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