heterogeneous catalyst

catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur

catalyst present in the same phase as the reactants

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Chemistry 2e · 12.7 Catalysis

Catalysis: practice problems

5 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 76
Account for the increase in reaction rate brought about by a catalyst.
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Exercises 78
Consider this scenario and answer the following questions: Chlorine atoms resulting from decomposition of chlorofluoromethanes, such as CCl₂F₂, catalyze the decomposition of ozone in the atmosphere. One simplified mechanism for the decomposition is:
$O_{3} \to sunlight O_{2} + O O_{3} + Cl ⟶ O_{2} + ClO ClO + O ⟶ Cl + O_{2}$
(a) Explain why chlorine atoms are catalysts in the gas-phase transformation:
$2 O_{3} ⟶ 3 O_{2}$
(b) Nitric oxide is also involved in the decomposition of ozone by the mechanism:
$O_{3} \to sunlight O_{2} + O O_{3} + NO ⟶ NO_{2} + O_{2} NO_{2} + O ⟶ NO + O_{2}$
Is NO a catalyst for the decomposition? Explain your answer.
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Exercises 80
For each of the following pairs of reaction diagrams, identify which of the pairs is catalyzed:
(a)
(b)
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Exercises 82
For each of the following reaction diagrams, estimate the activation energy (E $_{a}$ ) of the reaction:
(a)
(b)
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Exercises 84
Consider the similarities and differences in the two reaction diagrams shown in Exercise 12.82. Do these diagrams represent two different overall reactions, or do they represent the same overall reaction taking place by two different mechanisms? Explain your answer.
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Key terms · 2

heterogeneous catalyst: catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur
homogeneous catalyst: catalyst present in the same phase as the reactants

Learn 12.7 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 12.7 in the textbook · This section on openstax.org

Catalysis: practice problems

5 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 76

Account for the increase in reaction rate brought about by a catalyst.

Exercises 78

Consider this scenario and answer the following questions: Chlorine atoms resulting from decomposition of chlorofluoromethanes, such as CCl₂F₂, catalyze the decomposition of ozone in the atmosphere. One simplified mechanism for the decomposition is:

$O_{3} \to sunlight O_{2} + O O_{3} + Cl ⟶ O_{2} + ClO ClO + O ⟶ Cl + O_{2}$

(a) Explain why chlorine atoms are catalysts in the gas-phase transformation:

$2 O_{3} ⟶ 3 O_{2}$

(b) Nitric oxide is also involved in the decomposition of ozone by the mechanism:

$O_{3} \to sunlight O_{2} + O O_{3} + NO ⟶ NO_{2} + O_{2} NO_{2} + O ⟶ NO + O_{2}$

Is NO a catalyst for the decomposition? Explain your answer.

Exercises 80

For each of the following pairs of reaction diagrams, identify which of the pairs is catalyzed:

(a)

In this figure, two graphs are shown. The x-axes are labeled, “Extent of reaction” and the y-axes are labeled, “Energy (k J).” The y-axes are marked off from 0 to 50 at intervals of 5. In a, a blue curve is shown. It begins with a horizontal segment at about 2J. The curve then rises sharply near the middle to reach a maximum of about 46, then sharply falls to about 35, again rises to about 38 and falls to another horizontal segment at about 15. In b, the curve begins and ends similarly, but the first peak reaches about 46, drops to about 35, then rises to about 43 before falling to the horizontal region at about 15.

(b)

Exercises 82

For each of the following reaction diagrams, estimate the activation energy (E $_{a}$ ) of the reaction:

(a)

In this figure, a graph is shown. The x-axis is labeled, “Extent of reaction,” and the y-axis is labeled, “Energy (k J).” A blue curve is shown. It begins with a horizontal segment at about 35. The curve then rises sharply near the middle to reach a maximum of about 45, then sharply falls to about 24, again rises to about 30 and falls to another horizontal segment at about 15.

(b)

Exercises 84

Consider the similarities and differences in the two reaction diagrams shown in Exercise 12.82. Do these diagrams represent two different overall reactions, or do they represent the same overall reaction taking place by two different mechanisms? Explain your answer.

Key terms · 2

heterogeneous catalyst: catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur
homogeneous catalyst: catalyst present in the same phase as the reactants

Learn 12.7 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 12.7 in the textbook · This section on openstax.org