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Unformatted text preview: te or the activated complex of the slow step). • Mechanism is a model of how a reaction occurs.
o The slowest step of a mechanism is called the rate-determining step. o
Intermediates are species produced in earlier steps that are consumed in later
Transition state is an unstable arrangement in which the bonds are in the process
of being broken and formed and presents the maximum point on a potential energy
diagram; it can not be isolated.
o Mechanism must account for overall Stoichiometry, rate expression, etc. o Rate of overall reaction is the rate of the slowest step. o
Stoichiometry of an equation gives no information about the rate expression or
about the mechanism of a reaction. However any mechanism must be consistent with
overall Stoichiometry, rate expression, etc. For a 3rd order reaction, the first step
(containing a maximum of two particles) cannot be the slow, rate determining step. A Unimolecular step A Bimolecular step •
A unimolecular step involves a •
A bimolecular steps involves
single species as a reactant.
collision of two species (that form a
transition state or an activated complex
that can not be isolated).
Its rate law is therefore 1st order •
Its rate law is 1st order with respect to
with respect that reactant.
each of the colliding species and is
therefore 2nd order overall.
(N.B. Shading indicates Topic 16 (AHL) material.) © IBID Press 2007 3...
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This note was uploaded on 09/23/2010 for the course CS 001 taught by Professor Jix during the Spring '10 term at Riverside Community College.
- Spring '10