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

9. Alkenes and Alkynes

Hydrogenation of Alkynes

Organic Chemistry

9. Alkenes and Alkynes

Hydrogenation of Alkynes

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1:55 minutes

Problem 3

Textbook Question

What reaction would acetylene likely undergo if it were kept at 1500°C for too long?

Verified step by step guidance

Acetylene (C₂H₂) is a highly reactive alkyne with a triple bond between its two carbon atoms. At elevated temperatures, such as 1500 °C, it undergoes thermal decomposition or polymerization due to the instability of the molecule under such extreme conditions.

At 1500 °C, acetylene molecules can break apart into smaller fragments or recombine to form larger molecules. This process is driven by the high energy available at this temperature, which overcomes the bond dissociation energy of the triple bond.

One common reaction at this temperature is the formation of elemental carbon (C) and hydrogen gas (H₂). The reaction can be represented as:

C 2 H 2 \to C + H 2

Another possible reaction is the polymerization of acetylene to form benzene (C₆H₆) or other polycyclic aromatic hydrocarbons. This occurs when multiple acetylene molecules combine under high temperatures. For example:

3 C 2 H 2 \to C 6 H 6

In summary, if acetylene is kept at 1500 °C for too long, it is likely to undergo thermal decomposition into carbon and hydrogen gas or polymerization to form larger hydrocarbons such as benzene. These reactions are a result of the instability of acetylene at high temperatures.

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Key Concepts

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

Acetylene Structure and Properties

Acetylene (C2H2) is a simple alkyne characterized by a triple bond between two carbon atoms. This structure makes it highly reactive, particularly at elevated temperatures. Understanding its bonding and molecular geometry is crucial for predicting its behavior in chemical reactions.

Thermal Decomposition

At high temperatures, organic compounds like acetylene can undergo thermal decomposition, where the compound breaks down into simpler molecules or elements. This process can lead to the formation of carbon and hydrogen gas, as well as other hydrocarbons, depending on the conditions and duration of heating.

Combustion Reactions

Combustion reactions involve the reaction of a substance with oxygen, producing heat and light. Acetylene can combust at high temperatures, leading to the formation of carbon dioxide and water. Understanding combustion is essential for predicting the products and energy changes associated with heating acetylene.

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Related Practice

Textbook Question

Show how each of the following compounds can be prepared using the given starting material, any needed inorganic reagents, and any organic compound that has no more than four carbons:

Textbook Question

How can the following compounds be prepared using ethyne as the starting material?

Textbook Question

What are products of the following reactions?

Textbook Question

Show how you would convert

c. cis-cyclodecene to trans-cyclodecene.

Textbook Question

Hydration of alkynes (via oxymercuration) gives good yields of single compounds only with symmetrical or terminal alkynes. Show what the products would be from hydration of each compound.

d. cyclodecyne

Textbook Question

Predict the product of the following reactions.

(b)

Textbook Question

Describe the alkyne you should start with and the reagents you should use if you want to synthesize

b. cis-2-butene.

Textbook Question

Describe the alkyne you should start with and the reagents you should use if you want to synthesize

a. pentane.

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