Chemical Reaction Mechanisms and Catalysts

The video tutorial explains how reaction rates are determined, emphasizing the importance of experimental data. It introduces reaction mechanisms, detailing the steps from reactants to products, and explains molecularity. The tutorial covers intermediates, transition states, and how to determine rate laws using elementary steps. It concludes with a discussion on catalysts and their role in altering reaction speeds by lowering activation energy.

What is the primary reason we cannot determine the rate law from stoichiometry alone?

• Stoichiometry is not related to reaction speed.

• Stoichiometry is only used for balancing equations.

• Stoichiometry does not account for reaction mechanisms.

• Stoichiometry is only applicable to gaseous reactions.

What is molecularity in the context of reaction mechanisms?

• The speed at which a reaction occurs.

• The total number of steps in a reaction mechanism.

• The number of molecules that participate as reactants in an elementary reaction.

• The number of products formed in a reaction.

What happens to intermediates during a reaction?

• They are only present at the start of the reaction.

• They remain unchanged throughout the reaction.

• They are formed and consumed during the reaction.

• They are only present at the end of the reaction.

Why do we not work with transition states in reactions?

• They are too stable to be useful.

• They are only theoretical and do not exist in reality.

• They are too high in energy and do not last long enough.

• They are not involved in the reaction mechanism.

How can you identify the slow step in a reaction mechanism?

• It is the last step in the mechanism.

• It is the first step in the mechanism.

• It has the highest activation energy.

• It has the lowest activation energy.

What is the significance of the slow step in a reaction mechanism?

• It is the step with the least energy change.

• It is the step with the most reactants.

• It is the step where products are formed.

• It determines the overall reaction speed.

How can the rate law be determined from elementary steps?

• By calculating the total energy change.

• By using the stoichiometry of the slow step.

• By using the stoichiometry of the overall reaction.

• By measuring the temperature change.

What role does a catalyst play in a chemical reaction?

• It decreases the concentration of reactants.

• It increases the concentration of products.

• It increases the activation energy.

• It provides an alternative pathway with lower activation energy.

How can you identify a catalyst in a reaction?

• It only appears in the transition state.

• It is produced during the reaction.

• It is consumed during the reaction.

• It appears unchanged at the start and end of the reaction.

What is the effect of a catalyst on the speed of a reaction?

• It speeds up the reaction by increasing activation energy.

• It speeds up the reaction by lowering activation energy.

• It has no effect on the reaction speed.

• It slows down the reaction.