16.2.1 Explain that reactions can occur by more than one step and that the slowest step determines the rate of the reaction (rate-determining step)
- many reactions (especially more complicated ones) actually occur as a sequence of steps
- the "molecularity" of a reaction affects its reaction mechanism
- reactions with 3 molecules can be single step, more than 3 will always be multistep, and 2 or less may be multistep
- each of the steps in the sequence is called an elementary step
- each step involves no more than a trimolecular collision (it's usually unimolecular or bimolecular)
- the overall sequence is called the reaction mechanism
- reaction intermediates: products of one elementary step that are consumed in a later step
- catalyst: present at reaction start, may be used in an elementary step, but will be recreated in a later step (present at the end)
- the rate-determining step is the slowest step, which determines the rate of reaction
16.2.2 Describe the relationship between reaction mechanism, order of reaction, and rate-determining step
- the rate-determining step is the slowest in the series of elementary steps that constitute the mechanism of a reaction
- the rate law generally doesn't correspond to the balanced equation for the reaction (it only will if the reaction is single step)
- rate law of the overall reaction will be the rate law for the rate-determining step
- you may need to substitute other steps into the rate-determining step to get the rate law IF an intermediate is involved as a reactant in the rate-determining step but is not present as a reactant in the overall reaction