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Ch.6 - Thermochemistry
Tro - Chemistry: A Molecular Approach 4th Edition
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Tutti i libri di testoTro 4th EditionCh.6 - ThermochemistryProblema 73
Capitolo 6, Problema 73

When 0.514 g of biphenyl (C12H10) undergoes combustion in a bomb calorimeter, the temperature rises from 25.8 °C to 29.4 °C. Find ΔErxn for the combustion of biphenyl in kJ/mol biphenyl. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.86 kJ/°C.

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Identify the given values: mass of biphenyl = 0.514 g, initial temperature = 25.8 \(^\circ\)C, final temperature = 29.4 \(^\circ\)C, and heat capacity of the calorimeter = 5.86 kJ/\(^\circ\)C.
Calculate the change in temperature (\(\Delta T\)) using the formula \(\Delta T = T_{\text{final}} - T_{\text{initial}}\).
Determine the heat absorbed by the calorimeter (\(q_{\text{cal}}\)) using the formula \(q_{\text{cal}} = C_{\text{cal}} \times \Delta T\), where \(C_{\text{cal}}\) is the heat capacity of the calorimeter.
Since the reaction occurs in a bomb calorimeter, the heat absorbed by the calorimeter is equal to the negative of the change in internal energy of the reaction (\(\Delta E_{\text{rxn}}\)), so \(\Delta E_{\text{rxn}} = -q_{\text{cal}}\).
Convert \(\Delta E_{\text{rxn}}\) from kJ to kJ/mol by dividing by the number of moles of biphenyl. Calculate the moles of biphenyl using its molar mass (C_{12}H_{10}).

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Combustion Reaction

A combustion reaction is a chemical process in which a substance reacts rapidly with oxygen, producing heat and light. In this case, biphenyl (C12H10) combusts, releasing energy as it transforms into carbon dioxide and water. Understanding the stoichiometry of the reaction is essential for calculating the energy change associated with the combustion.
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Combustion Apparatus

Calorimetry

Calorimetry is the science of measuring the heat of chemical reactions or physical changes. In this scenario, a bomb calorimeter is used to measure the heat released during the combustion of biphenyl. The temperature change observed in the calorimeter, along with its heat capacity, allows for the calculation of the energy change (ΔErxn) for the reaction.
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Constant-Volume Calorimetry

Energy Change (ΔErxn)

ΔErxn represents the change in internal energy during a chemical reaction, typically expressed in kJ/mol. It quantifies the energy released or absorbed when a mole of a substance undergoes a reaction. In this case, calculating ΔErxn for biphenyl's combustion involves using the heat capacity of the calorimeter and the temperature change to determine the total energy released per mole of biphenyl combusted.
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Chemical Changes
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