Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

6. Thermodynamics and Kinetics

Energy Diagram

Organic Chemistry

6. Thermodynamics and Kinetics

Energy Diagram

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4:59 minutes

Problem 15

Textbook Question

(a) On a reaction coordinate diagram, show why a general, one-step reaction is faster when a catalyst is employed.
(b) Why does a catalyst often allow a reaction to proceed at lower temperatures?

Verified step by step guidance

To address part (a), start by understanding that a reaction coordinate diagram plots the energy of the system (y-axis) against the progress of the reaction (x-axis). In a one-step reaction, the diagram typically shows a single energy barrier (activation energy, Ea) that must be overcome for the reaction to proceed. A catalyst lowers this activation energy, which can be represented by a smaller peak on the diagram. This lower energy barrier means the reaction occurs faster because more molecules have sufficient energy to overcome the barrier at a given temperature.

For part (a), draw two reaction coordinate diagrams on the same graph. The first curve represents the uncatalyzed reaction with a higher activation energy (Ea). The second curve represents the catalyzed reaction with a lower activation energy. Ensure that the starting energy (reactants) and ending energy (products) remain the same for both curves, as a catalyst does not alter the thermodynamics of the reaction (ΔG, the free energy change).

To explain part (b), recall that the rate of a reaction depends on the number of molecules with sufficient energy to overcome the activation energy barrier. This relationship is described by the Arrhenius equation: \( k = A e^{-\frac{E_a}{RT}} \), where \( k \) is the rate constant, \( E_a \) is the activation energy, \( R \) is the gas constant, and \( T \) is the temperature. A lower activation energy (Ea) increases the rate constant (k), even at lower temperatures.

For part (b), explain that because a catalyst reduces the activation energy, the reaction can proceed efficiently at lower temperatures. This is particularly useful in industrial and biological processes where high temperatures may be impractical or damaging to sensitive materials.

Summarize by emphasizing that a catalyst accelerates a reaction by providing an alternative pathway with a lower activation energy, as shown in the reaction coordinate diagram, and this reduction in activation energy allows the reaction to occur at lower temperatures while maintaining a reasonable rate.

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Key Concepts

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

Reaction Coordinate Diagram

A reaction coordinate diagram visually represents the energy changes during a chemical reaction. It plots the potential energy of reactants and products against the progress of the reaction. The diagram illustrates the activation energy barrier that must be overcome for a reaction to occur, highlighting how catalysts lower this barrier, thus facilitating faster reactions.

Catalysis

Catalysis is the process by which a substance, known as a catalyst, increases the rate of a chemical reaction without being consumed in the process. Catalysts work by providing an alternative reaction pathway with a lower activation energy, allowing more reactant molecules to have sufficient energy to react, which is particularly important in one-step reactions.

Temperature and Reaction Rate

Temperature plays a crucial role in chemical reaction rates, as higher temperatures generally increase the kinetic energy of molecules, leading to more frequent and energetic collisions. Catalysts can enable reactions to occur at lower temperatures by lowering the activation energy, making it possible for the reaction to proceed efficiently even when the thermal energy is reduced.

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Textbook Question

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Textbook Question

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(a) On a reaction coordinate diagram, show why a general, one-step reaction is faster when a catalyst is employed.(b) Why does a catalyst often allow a reaction to proceed at lower temperatures?

Key Concepts

Reaction Coordinate Diagram

Catalysis

Temperature and Reaction Rate

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(a) On a reaction coordinate diagram, show why a general, one-step reaction is faster when a catalyst is employed.
(b) Why does a catalyst often allow a reaction to proceed at lower temperatures?