S.T.A.R.T: Chemical Catalytic Reaction

KNOWLEDGE CHECK: SHOW WHAT YOU KNOW!

Which of the following is true about a catalyst?

• (A) It speeds up a chemical reaction without being consumed.

• (B) It decreases the activation energy of a reaction.

• (C) It alters the equilibrium of the reaction.

• (D) Both A and B.

Answer explanation

Explanation: A catalyst speeds up a reaction without being consumed and decreases the activation energy, but it does not alter the reaction's equilibrium.

KNOWLEDGE CHECK: SHOW WHAT YOU KNOW

Which of the following factors is most important when selecting a catalyst for a chemical reaction?

• (A) The color of the catalyst.

• (B) The catalyst’s ability to increase the reaction rate without being consumed.

• (C) The size of the catalyst particles.

• (D) The cost of the catalyst.

Answer explanation

Explanation: The primary function of a catalyst is to speed up a reaction by lowering the activation energy, without being consumed or altered by the reaction itself. While cost and particle size may be important considerations, they are secondary to the catalyst's fundamental ability to affect the reaction rate. Color is irrelevant in catalyst selection unless it correlates with other properties, such as surface area or chemical composition.

KNOWLEDGE CHECK: SHOW WHAT YOU KNOW

Which of the following statements is the best describes the key difference between homogeneous and heterogeneous catalytic reactions?

• (A) Homogeneous catalysts operate in the same phase as the reactants, while heterogeneous catalysts operate in a different phase from the reactants.

• (B) Homogeneous catalysts are solid, while heterogeneous catalysts are liquid.

• (C) Homogeneous catalysts are less efficient than heterogeneous catalysts.

• (D) Homogeneous reactions do not involve catalysts, while heterogeneous reactions do.

Answer explanation

Explanation: In homogeneous catalysis, the catalyst is in the same phase (usually liquid or gas) as the reactants, allowing for uniform interaction. In heterogeneous catalysis, the catalyst is in a different phase (typically solid) from the reactants (which are often in liquid or gas form), with the reaction occurring on the surface of the catalyst. Other options are incorrect because they either misrepresent the physical state of the catalysts or do not accurately describe catalysis.

KNOWLEDGE CHECK: SHOW WHAT YOU KNOW

Which of the following attributes is most important when selecting a catalyst for a specific chemical reaction?

• (A) The catalyst’s selectivity for the desired product.

• (B) The catalyst’s ability to change the color of the reactants.

• (C) The size of the catalyst’s container.

• (D) The availability of the catalyst in large quantities.

Answer explanation

Explanation: Selectivity is crucial when choosing a catalyst because it ensures that the catalyst promotes the formation of the desired product while minimizing the production of unwanted by-products. This leads to a more efficient and cost-effective reaction. Attributes like the catalyst’s ability to change the color of reactants or the size of its container are irrelevant to its effectiveness, and while availability may be a practical consideration, it is secondary to the catalyst’s ability to perform the specific reaction selectively.

BRAIN TEASERS: WHAT'S YOUR BEST GUESS?

Increasing the temperature of a catalytic reaction always increases the reaction rate.

• True

• False

Answer explanation

Explanation: Increasing the temperature may increase the rate of reaction, but too high a temperature can deactivate the catalyst or cause undesirable side reactions.

BRAIN TEASERS: WHAT'S YOUR BEST GUESS?

Which of the following is correctly lists all the steps involved in a typical heterogeneous catalytic reaction?

• (A) Diffusion, Adsorption, Desorption

• (B) Adsorption, Surface Reaction, Desorption

• (C) Adsorption, Surface Reaction, Diffusion

• D) Surface Reaction, Desorption, Diffusion

Answer explanation

Explanation: In a heterogeneous catalytic reaction, reactants first adsorb onto the catalyst surface, undergo a surface reaction, and then desorb as products.

BRAIN TEASERS: WHAT'S YOUR BEST GUESS?

Which of the following steps do you think that is usually the rate-limiting step in a heterogeneous catalytic reaction?

• (A) Adsorption of reactants

• (B) Surface reaction

• (C) Desorption of products

• (D) Diffusion of reactants to the surface

Answer explanation

Explanation: In many cases, the surface reaction step is the slowest and limits the overall rate of the reaction.

BRAIN TEASERS: WHAT'S YOUR BEST GUESS?

Why is it important to understand the Langmuir-Hinshelwood mechanism in heterogeneous catalysis?

• (A) It helps explain the rate-determining step in reactions involving both adsorption and surface reactions.

• (B) It describes the relationship between pressure and the volume of gases in a reaction.

• (C) It helps predict the color changes in catalysts during reactions.

• (D) It explains how homogeneous reactions occur in a liquid phase.

Answer explanation

Explanation: The Langmuir-Hinshelwood mechanism is crucial in heterogeneous catalysis because it provides a detailed model for how reactants adsorb onto a catalyst’s surface, react, and then desorb as products. This mechanism helps chemists and engineers understand the rate-determining steps in such reactions and optimize conditions for better catalytic performance. Options (B), (C), and (D) are unrelated to the mechanism, as it specifically deals with adsorption and surface reactions, not gas laws, color changes, or homogeneous reactions.

BRAIN TEASERS: WHAT'S YOUR BEST GUESS?

How does the Langmuir-Hinshelwood mechanism assist in the application of chemical engineering processes in industry?

• (A) It allows engineers to predict and control the rates of surface-catalyzed reactions by understanding how reactants adsorb, react, and desorb on a catalyst.

• (B) It helps determine the structural composition of catalysts used in homogeneous reactions.

• (C) It provides guidelines for minimizing energy consumption in chemical plants by regulating pressure and temperature.

• (D) It focuses on the design of reactors that operate without any form of catalysis.

Answer explanation

Explanation: The Langmuir-Hinshelwood mechanism is central to chemical engineering applications because it offers a clear model for surface-catalyzed reactions, helping engineers optimize catalytic processes. By understanding how reactants adsorb onto the catalyst, undergo surface reactions, and desorb as products, engineers can improve reaction rates, selectivity, and efficiency in industrial catalytic processes such as refining, chemical synthesis, and environmental protection. Options (B), (C), and (D) do not accurately reflect the specific contributions of the Langmuir-Hinshelwood mechanism to surface catalysis and industrial applications.

BRAIN TEASERS: WHAT'S YOUR BEST GUESS?

Which of the following is a common cause of catalyst deactivation in industrial chemical processes?

• (A) Excessive catalyst surface area.

• (B) Sintering of catalyst particles due to high temperatures.

• (C) Use of too much catalyst in the reactor.

• (D) Overuse of reactants in the chemical process.

Answer explanation

Explanation: Catalyst deactivation can occur for several reasons, with sintering being a key cause. Sintering is the process where catalyst particles agglomerate or fuse at high temperatures, reducing the active surface area available for reactions and diminishing catalyst efficiency. Other causes of deactivation include poisoning (by contaminants like sulfur or carbon deposits) and fouling (where catalyst pores are blocked). Options (A), (C), and (D) do not directly cause catalyst deactivation in the same way that sintering or other specific mechanisms like poisoning or fouling do.