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Multiple Choice
When 1.550 g of liquid hexane (C6H14) undergoes combustion in a bomb calorimeter, the temperature rises from 25.87 °C to 38.13 °C. If the heat capacity of the bomb calorimeter is 5.73 kJ/°C, what is the ΔErxn for the reaction in kJ/mol hexane?
A
-5000 kJ/mol
B
-3500 kJ/mol
C
-4160 kJ/mol
D
-2500 kJ/mol
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1
Identify the given values: mass of hexane (1.550 g), initial temperature (25.87 °C), final temperature (38.13 °C), and heat capacity of the calorimeter (5.73 kJ/°C).
Calculate the temperature change (ΔT) by subtracting the initial temperature from the final temperature: ΔT = 38.13 °C - 25.87 °C.
Use the formula q = C * ΔT to calculate the heat absorbed by the calorimeter, where q is the heat absorbed, C is the heat capacity, and ΔT is the temperature change.
Convert the mass of hexane to moles using its molar mass (C6H14 has a molar mass of approximately 86.18 g/mol).
Calculate the ΔErxn (change in internal energy for the reaction) per mole of hexane by dividing the heat absorbed by the number of moles of hexane. Remember to account for the sign, as combustion is an exothermic process.