Chemical Kinetics and Reaction Mechanisms
What Controls Reaction Rate?
Kinetic View of Chemistry
Reaction rate depends on collision frequency, orientation, activation energy, and the pathway connecting reactants to products. Catalysts lower the effective activation energy without changing the overall free-energy difference.
Kinetic Terms
What is the main effect of a catalyst?
A catalyst provides a lower-energy pathway and speeds both forward and reverse reactions.
Correct answer: It lowers the activation energy
Does a catalyst change the equilibrium position? Answer yes or no.
Catalysts do not alter the thermodynamic equilibrium constant; they only help the system reach equilibrium faster.
Correct answer: no
Elementary Steps and Rate-Determining Steps
Mechanistic Reasoning
A mechanism is a sequence of elementary steps. The slowest step often controls the rate and is called the rate-determining step. Mechanistic proposals must be consistent with the observed rate law and intermediates.
Which statement about an intermediate is correct?
Intermediates are formed and then consumed during the mechanism and do not appear in the overall reaction.
Correct answer: It is consumed in one step and produced in another
What is the purpose of a reaction mechanism?
Mechanisms explain how reactants are converted to products through elementary steps.
Correct answer: to describe the stepwise molecular pathway of a reaction