Textbook Question
Acetylene (H–C≡C–H) is the fuel used in welding torches.
b. Estimate ∆H for this reaction (in kJ/mol) using the bond energies listed in Table 7.1.
Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 7, Problem 25a
The vaporization of Br2 from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol).
a. What is the sign of ∆H for this process? Write a reaction showing heat as a product or reactant.
Verified step by step guidance1
Understand the concept of enthalpy change (∆H): Enthalpy change is the heat absorbed or released during a chemical or physical process at constant pressure. For endothermic processes, ∆H is positive, and for exothermic processes, ∆H is negative.
Identify the type of process: Vaporization is the process of converting a liquid into a gas. This requires energy input to overcome intermolecular forces, making it an endothermic process. Therefore, the sign of ∆H is positive.
Write the reaction for the vaporization of bromine (Br₂): The reaction can be written as Br₂(l) → Br₂(g).
Include heat in the reaction: Since the process is endothermic, heat is absorbed. Heat is written as a reactant in the reaction: Br₂(l) + heat → Br₂(g).
Summarize: The sign of ∆H for the vaporization of Br₂ is positive, and the reaction showing heat as a reactant is Br₂(l) + heat → Br₂(g).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enthalpy Change (∆H)
Enthalpy change (∆H) is a measure of the heat content of a system during a process at constant pressure. A positive ∆H indicates that heat is absorbed from the surroundings, while a negative ∆H signifies that heat is released. In the context of vaporization, the process requires energy input, resulting in a positive ∆H.
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Physical & Chemical Changes
Endothermic Process
An endothermic process is one that absorbs heat from its surroundings. In the case of vaporization, the transition of a substance from liquid to gas requires energy to overcome intermolecular forces. This absorption of heat is reflected in the positive value of ∆H, indicating that heat is a reactant in the reaction.
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Chemical Reaction Representation
Chemical reactions can be represented with a balanced equation that includes reactants, products, and energy changes. For the vaporization of bromine (Br2), the reaction can be written as: Br2(l) + heat → Br2(g). This notation emphasizes that heat is required for the transition from liquid to gas, highlighting the endothermic nature of the process.
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Related Practice
Textbook Question
Is the total enthalpy (H) of the reactants for an endothermic reaction greater than or less than the total enthalpy of the products?
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Textbook Question
The vaporization of Br2 from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol).
c. How many kilojoules are needed to evaporate 82 g of Br2?
Textbook Question
The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).
b. Is the reaction likely to be spontaneous at all temperatures, nonspontaneous at all temperatures, or spontaneous at some but nonspontaneous at others?
Textbook Question
Converting liquid water to solid ice releases 1.44 kcal/mol (6.02 kJ/mol).How many kilocalories are released by freezing 32 g of H2O?
Textbook Question
The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).
a. What is the sign of ∆S for the reaction?