1.5: Reaction Mehcanisms, Catalysis, and Rate Laws

What is a reaction mechanism?

A series of steps that may be added together to give and overall chemical reaction.

What is an elementary process

Each individual step in a mechanism

What is the molecularity of an elementary process

The number of reactant species that must collide to produce the reaction indicated by that step

unimolecular

reaction involving one molecule

bimolecular

reaction involving the collision of two molecules

termolecular

reaction involving 3 molecules (extremely rare)

What could speces that aren’t reactants or products be?

an intermediate or a catalyst

intermediate

a species that is formed in one step and is consumed int he subsequent step

catalyst

a species consumed in one stop and regenerated in a subsequent or later step

What does a catalyst do

it provides an alternate, lower energy pathways and this pathway is actually a different reaction mechanism

What is the rate determining step?

The slowest elementary process

Why can’t the overall reaction rate exceed the slowest elementary process?

Because its like a limiting reagent. it determines the reaction rate

What conidtions can cause a step to limit the reaction?

• complex collision geometry

• high activation energy

• low concentrations of reactants

• a termolecular collision

How would you increase the reaction rate for a reaction with multiple elementary processes?

Identify the rate determining step, which is the slowest, and increase the concetration of reactants in that step/ adjusting factors which increase reaction rate

How to calculate OVERALL activation energyy

Difference between the potential energy of the activated complex with the highest energy and the potential energy of the reactants as a whole