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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4:08 minutes

Problem 13b,c

Textbook Question

When a small piece of platinum is added to a mixture of ethene and hydrogen, the following reaction occurs:

Doubling the concentration of hydrogen has no effect on the reaction rate. Doubling the concentration of ethene also has no effect.
b. Write the unusual rate equation for this reaction.
c. Explain this strange rate equation, and suggest what one might do to accelerate the reaction.

Verified step by step guidance

Step 1: Analyze the reaction. The reaction involves the hydrogenation of ethene (C₂H₄) to ethane (C₂H₆) using hydrogen gas (H₂) in the presence of a platinum catalyst. The platinum catalyst facilitates the addition of hydrogen atoms to the double bond in ethene, converting it into a single bond in ethane.

Step 2: Understand the rate equation. The problem states that doubling the concentration of hydrogen or ethene has no effect on the reaction rate. This suggests that the reaction rate is independent of the concentrations of the reactants, which is unusual for a typical chemical reaction. The rate equation for this reaction can be written as: rate = k, where k is the rate constant.

Step 3: Explain the unusual rate equation. The independence of the reaction rate from the concentrations of ethene and hydrogen indicates that the reaction is likely limited by the surface area of the platinum catalyst. The catalyst provides active sites for the reaction, and once these sites are saturated, increasing the concentration of reactants does not increase the rate.

Step 4: Suggest a way to accelerate the reaction. To increase the reaction rate, one could increase the surface area of the platinum catalyst. This can be achieved by using finely divided platinum or a platinum catalyst supported on a porous material, which provides more active sites for the reaction.

Step 5: Summarize the findings. The reaction rate is determined by the availability of active sites on the platinum catalyst rather than the concentrations of the reactants. Enhancing the catalyst's surface area is the most effective way to accelerate the reaction.

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Key Concepts

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

Reaction Rate and Rate Laws

The reaction rate refers to the speed at which reactants are converted into products in a chemical reaction. Rate laws express the relationship between the concentration of reactants and the rate of the reaction. They are determined experimentally and can indicate how changes in concentration affect the rate, often represented as rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to reactants A and B.

Catalysis

Catalysis involves the acceleration of a chemical reaction by a substance called a catalyst, which is not consumed in the reaction. In this case, platinum serves as a heterogeneous catalyst, facilitating the reaction between ethene and hydrogen without altering its own structure. Catalysts lower the activation energy required for a reaction, allowing it to proceed more quickly, but they do not change the overall stoichiometry of the reaction.

Zero-Order Reactions

A zero-order reaction is one where the rate of reaction is independent of the concentration of the reactants. This means that even if the concentration of ethene or hydrogen is doubled, the reaction rate remains unchanged. This behavior often occurs when a catalyst is present, and the reaction is limited by the surface area of the catalyst rather than the concentration of the reactants. To accelerate a zero-order reaction, one might increase the surface area of the catalyst or increase the temperature.

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Textbook Question

The following reaction is a common synthesis used in the organic chemistry laboratory course.

When we double the concentration of methoxide ion (CH₃O^–), we find that the reaction rate doubles. When we triple the concentration of 1-bromobutane, we find that the reaction rate triples.

a. What is the order of this reaction with respect to 1-bromobutane? What is the order with respect to methoxide ion? Write the rate equation for this reaction. What is the overall order?

Textbook Question

Deuterium (D) is the hydrogen isotope of mass number 2, with a proton and a neutron in its nucleus. The chemistry of deuterium is nearly identical to the chemistry of hydrogen, except that the C―D bond is slightly stronger than the C―H bond by 5.0 kJ/mol (1.2 kcal/mol). Reaction rates tend to be slower when a C―D bond (as opposed to a C―H bond) is broken in a rate-limiting step.

This effect, called a kinetic isotope effect, is clearly seen in the chlorination of methane. Methane undergoes free-radical chlorination 12 times as fast as tetradeuteriomethane (CD₄).

b. Monochlorination of deuterioethane (C₂H₅D) leads to a mixture containing 93% C₂H₄DCl and 7% C₂H₅Cl. Calculate the relative rates of abstraction per hydrogen and deuterium in the chlorination of deuterioethane.

Textbook Question

Treatment of tert-butyl alcohol with concentrated HCl gives tert-butyl chloride.

When the concentration of H⁺ is doubled, the reaction rate doubles. When the concentration of tert-butyl alcohol is tripled, the reaction rate triples. When the chloride ion concentration is quadrupled, however, the reaction rate is unchanged. Write the rate equation for this reaction.

Textbook Question

Under certain conditions, the reaction of 0.5 M 1-bromobutane with 1.0 M sodium methoxide forms 1-methoxybutane at a rate of 0.05 mol/L per second. What would be the rate if 0.1 M 1-bromobutane and 2.0 M NaOCH₃ were used?

Textbook Question

How will the rate of the reaction between bromomethane and hydroxide ion be affected if the following changes in concentration are made?

c. The concentration of the alkyl halide is cut in half and the concentration of the nucleophile is doubled.

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?

Textbook Question

For the following acid–base pairs, (v) show a mechanism for the reaction; and (vi) draw a reaction coordinate diagram.

(f)

Textbook Question

Identify the nucleophile and the electrophile in the following acid–base reactions:

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