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Ch.6 - Thermochemistry
All textbooksTro 4th EditionCh.6 - ThermochemistryProblem 106
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Chapter 6, Problem 106

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Use standard enthalpies of formation to calculate the amount of heat released per kilogram of methanol fuel and per kilogram of hydrogen fuel.

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1
Identify the chemical reactions for the combustion of methanol (CH₃OH) and hydrogen (H₂).
Write the balanced chemical equations for the combustion reactions: CH₃OH + 1.5O₂ → CO₂ + 2H₂O and 2H₂ + O₂ → 2H₂O.
Use standard enthalpies of formation (ΔH_f°) to calculate the enthalpy change (ΔH_rxn) for each reaction. ΔH_rxn = ΣΔH_f°(products) - ΣΔH_f°(reactants).
Determine the molar mass of methanol and hydrogen to convert the enthalpy change from per mole to per kilogram.
Calculate the heat released per kilogram by dividing the enthalpy change by the molar mass for each fuel.
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Related Practice
Open Question
Calculate the caloric content of table sugar (sucrose, C12H22O11), given that the standard enthalpy of formation of sucrose is -2226.1 kJ/mol. For comparison, the standard enthalpy of formation of palmitic acid (C16H32O2), a dietary fat found in beef and butter, is -208 kJ/mol. Use H2O(l) in the balanced chemical equations, as the metabolism of these compounds produces liquid water.
Textbook Question

Palmitic acid (C16H32O2) is a dietary fat found in beef and butter. The caloric content of palmitic acid is typical of fats in general. Write a balanced equation for the complete combustion of palmitic acid and calculate the standard enthalpy of combustion. What is the caloric content of palmitic acid in Cal/g? The standard enthalpy of formation of palmitic acid is -208 kJ/mol and that of sucrose is -2226.1 kJ/mol. [Use H2O(l) in the balanced chemical equations because the metabolism of these compounds produces liquid water.]

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Textbook Question

Palmitic acid (C16H32O2) is a dietary fat found in beef and butter. The caloric content of palmitic acid is typical of fats in general. Which dietary substance (sugar or fat) contains more Calories per gram? The standard enthalpy of formation of palmitic acid is -208 kJ/mol and that of sucrose is -2226.1 kJ/mol. [Use H2O(l) in the balanced chemical equations because the metabolism of these compounds produces liquid water.]

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Textbook Question

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Which fuel contains the most energy in the least mass?

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Textbook Question

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. How does the energy of these fuels compare to that of octane (C8H18)? 

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Open Question
Derive a relationship between ΔH and ΔE for a process in which the temperature of a fixed amount of an ideal gas changes.