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Ch.14 - Chemical Kinetics
All textbooksBrown 14th EditionCh.14 - Chemical KineticsProblem 76
Chapter 14, Problem 76

b) What role does adsorption play in the action of a heterogeneous catalyst?

Verified step by step guidance
1
Understand the concept of adsorption: Adsorption is the process by which atoms, ions, or molecules from a substance (such as a gas, liquid, or dissolved solid) adhere to a surface of the adsorbent. This is a surface phenomenon and is different from absorption, where a substance diffuses into a liquid or solid to form a solution.
Identify the role of a heterogeneous catalyst: A heterogeneous catalyst is in a different phase than the reactants, typically solid catalysts in contact with gaseous or liquid reactants. The catalyst provides a surface for the reaction to occur, which can lower the activation energy and increase the reaction rate.
Explain how adsorption is involved: In the action of a heterogeneous catalyst, adsorption is crucial because it allows reactant molecules to adhere to the surface of the catalyst. This proximity facilitates the breaking and forming of chemical bonds, which is necessary for the reaction to proceed.
Discuss the effect of adsorption on reaction rate: The adsorption of reactants onto the catalyst surface increases the concentration of reactants at the surface, enhancing the likelihood of collisions and interactions that lead to the formation of products. This effectively increases the reaction rate.
Conclude with the desorption process: After the reaction occurs on the catalyst surface, the products are desorbed, or released, from the surface, freeing up the active sites on the catalyst for new reactant molecules to be adsorbed and react. This cycle of adsorption, reaction, and desorption is continuous, allowing the catalyst to be reused multiple times.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Adsorption

Adsorption is the process by which atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to a surface. In heterogeneous catalysis, reactants are adsorbed onto the surface of the catalyst, which increases the local concentration of reactants and facilitates their interaction, leading to a higher reaction rate.

Heterogeneous Catalysis

Heterogeneous catalysis involves a catalyst that is in a different phase than the reactants, typically solid catalysts interacting with gaseous or liquid reactants. This phase difference allows for easier separation of the catalyst from the products and often results in more efficient reactions due to the increased surface area available for adsorption.
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Reaction Mechanism

The reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. In the context of heterogeneous catalysis, understanding the mechanism is crucial as it reveals how adsorption, surface reactions, and desorption contribute to the overall efficiency and selectivity of the catalyst.
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Related Practice
Textbook Question

You have studied the gas-phase oxidation of HBr by O2: 4 HBr(g) + O2(g) → 2 H2O(g) + 2 Br2(g)

You find the reaction to be first order with respect to HBr and first order with respect to O2. You propose the following mechanism:

HBr(g) + O2(g) → HOOBr(g)

HOOBr(g) + HBr(g) → 2 HOBr(g)

HOBr(g) + HBr(g) → H2O(g) + Br2(g)

(b) Based on the experimentally determined rate law, which step is rate determining?

Textbook Question

(a) What is a catalyst? (b) What is the difference between a homogeneous and a heterogeneous catalyst?

Textbook Question

(c) Do catalysts affect the overall enthalpy change for a reaction, the activation energy, or both?

Textbook Question

(a) Most commercial heterogeneous catalysts are extremely finely divided solid materials. Why is particle size important?