Unit 5: Topic 11 - Catalysis

Question 1

Describe what occurs in catalysis.

Answer 1

Catalysis increases the rate of a specific reaction through the addition of a “catalyst,” which are compounds that are not consumed in the reaction and remain in their original state after the reaction proceeds. The catalyst can either decrease the activation energy of the original reaction without affecting ∆H (as shown here), or it can increase the number of effective collisions in the reaction so that the reaction can proceed faster.

Question 2

The reaction 2SO2 + O2 –> 2SO3 can be catalyzed by nitric oxide, NO, and the resulting reaction proceeds in two steps as shown here. Explain why the concentration of the catalyst NO remains constant even though it reacts and is regenerated, and explain how NO could catalyze this reaction.

Answer 2

As can be seen in the alternate mechanism, nitric oxide will react in the first step to produce an intermediate, which will further react to reproduce the nitric oxide in equal amounts. The concentration of NO stays the same after the reaction because it is not consumed. Additionally, this alternate reaction mechanism has a lower activation energy than the original reaction, so NO acts as a catalyst.

Question 3

How are enzymes important in catalysis?

Answer 3

Enzymes are biological catalysts. In biological reactions, enzymes can bond with reactants and reorient them in a more favorable way to lower activation energy; the new reaction can be millions of times faster.

Question 4

The decomposition of sucrose into fructose and glucose can be catalyzed by a proton or an acid. The resulting mechanism is shown here. Explain how the catalyst speeds up the reaction rate in this specific reaction.

Answer 4

The catalyst, H+, will covalently bond to sucrose (the reactant) in the first step of the new reaction mechanism. The new reaction intermediate is now the protonated sucrose. This is another example of a reaction where the catalyst reacts with and bonds to a reactant but is regenerated, and the new reaction mechanism has a lower activation energy than the initial reaction.

Question 5

Define adsorption and explain its importance in surface catalysis.

Answer 5

Adsorption is defined to be the adhesion of atoms, molecules, or ions from a gas, liquid, or dissolved solid to a surface. Adsorption is important in surface catalysis because it allows for reactant molecules to be absorbed onto a solid surface before they react with the catalyst to form products.