Textbook Question
Ethanol (C2H5OH) is blended with gasoline as an automobile fuel. (d) Calculate the mass of CO2 produced per kJ of heat emitted.
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Ch.5 - Thermochemistry
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement111
- Ch.2 - Atoms, Molecules, and Ions166
- Ch.3 - Chemical Reactions and Reaction Stoichiometry138
- Ch.4 - Reactions in Aqueous Solution127
- Ch.5 - Thermochemistry104
- Ch.6 - Electronic Structure of Atoms109
- Ch.7 - Periodic Properties of the Elements107
- Ch.8 - Basic Concepts of Chemical Bonding102
- Ch.9 - Molecular Geometry and Bonding Theories120
- Ch.10 - Gases122
- Ch.11 - Liquids and Intermolecular Forces79
- Ch.12 - Solids and Modern Materials102
- Ch.13 - Properties of Solutions99
- Ch.14 - Chemical Kinetics153
- Ch.15 - Chemical Equilibrium83
- Ch.16 - Acid-Base Equilibria109
- Ch.17 - Additional Aspects of Aqueous Equilibria117
- Ch.18 - Chemistry of the Environment60
- Ch.19 - Chemical Thermodynamics109
- Ch.20 - Electrochemistry113
- Ch.21 - Nuclear Chemistry79
- Ch.22 - Chemistry of the Nonmetals52
- Ch.23 - Transition Metals and Coordination Chemistry57
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry7
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
Chapter 5, Problem 82b
Methanol (CH3OH) is used as a fuel in race cars. (b) Calculate the standard enthalpy change for the reaction, assuming H2O(g) as a product.
Verified step by step guidance1
Determine the balanced chemical equation for the combustion of methanol (CH_3OH). The general form is: CH_3OH(l) + O_2(g) -> CO_2(g) + H_2O(g).
Balance the equation by ensuring the number of atoms of each element is the same on both sides. For methanol combustion, it becomes: 2 CH_3OH(l) + 3 O_2(g) -> 2 CO_2(g) + 4 H_2O(g).
Use standard enthalpy of formation values (ΔH_f^°) for each compound involved in the reaction. These values are typically found in a table of thermodynamic data.
Apply Hess's Law to calculate the standard enthalpy change (ΔH_rxn^°) for the reaction: ΔH_rxn^° = [Σ ΔH_f^°(products)] - [Σ ΔH_f^°(reactants)].
Substitute the ΔH_f^° values into the equation and perform the arithmetic to find the standard enthalpy change for the reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Standard Enthalpy Change
Standard enthalpy change (ΔH°) refers to the heat change that occurs at constant pressure when one mole of a substance is formed from its elements in their standard states. It is a crucial concept in thermodynamics, allowing chemists to predict the energy changes associated with chemical reactions. This value is typically measured in kilojoules per mole (kJ/mol) and is essential for calculating the energy released or absorbed during a reaction.
Combustion Reactions
Combustion reactions involve the reaction of a substance with oxygen, producing heat and light. In the case of methanol (CH₃OH), its combustion with oxygen yields carbon dioxide (CO₂) and water (H₂O) as products. Understanding the stoichiometry of combustion reactions is vital for calculating the enthalpy change, as it allows for the determination of the amount of reactants and products involved in the reaction.
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Combustion Apparatus
Hess's Law
Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle is useful for calculating the standard enthalpy change of a reaction when direct measurement is difficult. By using known enthalpy values of related reactions, one can derive the enthalpy change for the desired reaction, such as the combustion of methanol.
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Related Practice
Textbook Question
Methanol (CH3OH) is used as a fuel in race cars. (c) Calculate the heat produced by combustion per liter of methanol. Methanol has a density of 0.791 g/mL.
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Textbook Question
Ethanol (C2H5OH) is blended with gasoline as an automobile fuel. (c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of 0.789 g/mL.
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Textbook Question
Ethane, C2H6, is an alkane with one C─C bond and six C─H bonds (Section 2.9). a. Use enthalpies of formation given in Appendix C to calculate Δ𝐻 for the reaction C2H6(𝑔)→2C(𝑔)+6H(𝑔). b. Use the result from part (a) and the value of 𝐷(C─H) from Table 5.4 to estimate the bond enthalpy 𝐷(C─C). c. How large is the difference between the value calculated for in part (b) and the value given in Table 5.4?
Textbook Question
Methanol (CH3OH) is used as a fuel in race cars. (d) Calculate the mass of CO2 produced per kJ of heat emitted.
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Textbook Question
Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest–burning octanes is a compound called 2,3,4- trimethylpentane, which has the following structural formula: The complete combustion of one mole of this compound to CO2(g) and H2O(g) leads to ΔH° = -5064.9 kJ. (b) By using the information in this problem and data in Table 5.3, calculate H°f for 2,3,4-trimethylpentane.
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