1/31/2024 MECHANISMS & CATALYSIS Flashcards
Define Reaction Mechanism.
A set of steps that describes how a reaction occurs at the molecular level. (must be consistent with the rate law for the reaction)
What is the Rate-Limiting or Rate-Determining Step?
The slowest elementary step in a chemical reaction, and the rate of this step controls the overall reaction rate. (The molecularity of this step should therefore define the rate constant expression for the overall reaction)
What is Molecularity? Define unimolecular, bimolecular and termolecular.
The number of molecules (or atoms or ions) involved in an elementary step in a reaction.
- unimolecular:
A->B+C - bimolecular:
A+B->C+D - termolecular (RARE):
A+B+C->D - Be suspicious! Mechanism is most likely present
How do you tell which is the Intermediate in a reaction?
INTERMEDIATE: Product in the first elementary reaction and reactant in the second elementary reaction.
How do you tell which is the Catalyst in a reaction?
CATALYST: Present in the first elementary reaction but used up
How do catalytic converters reduce emissions?
They reduce the activation energy required to decompose NO into N2 and O2.
What is a homogeneous catalyst?
Occurs in the same phase as the reacting molecules
What is a heterogeneous catalyst?
Exists in a different phase from the reactant molecules.
Do we write rate laws based on intermediates?
NO!
From which elementary step is the rate law determined?
THE SLOWEST (determining step)
