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 26
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?
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Determine the molar mass of H2O. The molar mass of H2O is calculated by adding the atomic masses of 2 hydrogen atoms and 1 oxygen atom.
Calculate the number of moles of H2O in 32 g. Use the formula: \( \text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \).
Use the given energy release per mole to find the total energy released. Multiply the number of moles by the energy released per mole (1.44 kcal/mol).
Ensure the units are consistent and the final answer is in kilocalories.
Review the calculation to ensure all steps are correctly followed and the units are properly converted if necessary.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molar Mass of Water
The molar mass of water (H2O) is approximately 18 g/mol. This value is essential for converting grams of water to moles, which is necessary for calculating the energy released during the phase change from liquid to solid.
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Calculating Molar Mass
Phase Change and Latent Heat
Phase change refers to the transition of a substance from one state of matter to another, such as from liquid to solid. The latent heat of fusion for water is the amount of energy released when water freezes, quantified as 1.44 kcal/mol, which is crucial for determining the total energy released when a specific mass of water freezes.
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Energy Calculation
To find the total energy released during the freezing of water, one must calculate the number of moles in the given mass and then multiply by the latent heat of fusion. This involves using the formula: Energy = moles × latent heat, which provides the total energy in kilocalories for the specified mass of water.
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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
Nitrogen in air reacts at high temperatures to form NO2 according to the following reaction: N2 + 2 O2 → 2 NO2
b. Estimate ∆H for this reaction (in kcal and kJ) using the bond energies from Table 7.1.
Textbook Question
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.
Textbook Question
Glucose, also known as "blood sugar" when measured in blood, has the formula C6H12O6.
a. Write the equation for the combustion of glucose with O2 to give CO2 and H2O.