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Ch.7 - Thermochemistry
Tro - Chemistry: A Molecular Approach 5th Edition
Tro5th EditionChemistry: A Molecular ApproachISBN: 9780134874371Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoTro 5th EditionCh.7 - ThermochemistryProblema 106
Capitolo 7, Problema 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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Standard Enthalpy of Formation

The standard enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It is a crucial value used in thermodynamics to calculate the heat released or absorbed during chemical reactions. For fuels like methanol and hydrogen, these values help determine their energy content and efficiency as alternatives to hydrocarbon fuels.
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02:34
Enthalpy of Formation

Heat of Combustion

The heat of combustion is the amount of energy released when a substance undergoes complete combustion with oxygen. This value is essential for evaluating the energy efficiency of fuels. By comparing the heat of combustion of methanol and hydrogen, one can assess which fuel releases more energy per kilogram, aiding in the selection of alternative fuels.
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02:24
Combustion Apparatus

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on the balanced chemical equations. It is vital for determining the amount of heat released per kilogram of fuel, as it allows for the conversion of moles of fuel to mass and the calculation of energy changes during combustion. Understanding stoichiometry is essential for accurate thermodynamic calculations in fuel analysis.
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Stoichiometry Concept
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