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Ch.5 - Thermochemistry
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 14th EditionCh.5 - ThermochemistryProblema 44b
Capitolo 5, Problema 44b

Consider the following reaction: 2 CH3OH(g) → 2 CH4(g) + O2(g) ΔH = +252.8 kJ (b) Calculate the amount of heat transferred when 24.0 g of CH3OH(g) is decomposed by this reaction at constant pressure.

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Determine the molar mass of CH_3OH by adding the atomic masses of its constituent atoms: C (12.01 g/mol), H (1.01 g/mol), and O (16.00 g/mol).
Calculate the number of moles of CH_3OH in 24.0 g by dividing the mass by the molar mass.
Use the stoichiometry of the reaction to relate the moles of CH_3OH to the enthalpy change (ΔH). The reaction shows that 2 moles of CH_3OH correspond to an enthalpy change of +252.8 kJ.
Calculate the heat transferred for the moles of CH_3OH you have by setting up a proportion based on the stoichiometry: (moles of CH_3OH / 2 moles) = (x kJ / 252.8 kJ).
Solve for x to find the amount of heat transferred when 24.0 g of CH_3OH is decomposed.

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Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced equation. It allows us to determine the relationships between the quantities of substances involved in a reaction. In this case, knowing the molar ratios from the balanced equation helps us convert grams of CH₃OH to moles, which is essential for calculating heat transfer.
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Stoichiometry Concept

Enthalpy Change (ΔH)

Enthalpy change (ΔH) represents the heat absorbed or released during a chemical reaction at constant pressure. A positive ΔH indicates that the reaction is endothermic, meaning it absorbs heat from the surroundings. In this reaction, ΔH = +252.8 kJ signifies that 252.8 kJ of heat is required to decompose 2 moles of CH₃OH, which is crucial for calculating the heat transferred for a specific mass.
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Enthalpy of Formation

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between the mass of a substance and the number of moles. For CH₃OH, the molar mass is approximately 32.04 g/mol, which allows us to calculate how many moles are present in 24.0 g, facilitating the determination of the heat transferred in the reaction.
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