The temperature rises from 25.00 °C to 29.00 °C when 3.50 g of sucrose undergoes combustion in a bomb calorimeter. Calculate U for the combustion of sucrose in kJ sucrose. The heat capacity of the calorimeter is 4.90 kJ . The molar mass of sugar is 342.3 g .

Question

The temperature rises from 25.00 °C to 29.00 °C when 3.50 g of sucrose undergoes combustion in a bomb calorimeter. Calculate  U for the combustion of sucrose in kJ  sucrose. The heat capacity of the calorimeter is 4.90 kJ  . The molar mass of sugar is 342.3 g  .

Quizplus · Accepted Answer

First, let's calculate the amount of heat released by sucrose during combustion:
q = msΔT = 3.50 g * 4.18 J/g°C * (29.00-25.00) °C = 583.6 J
Next, let's convert this to kJ and divide by the amount of sucrose burned:
ΔU = -q/n = -583.6 J / (3.50/342.3 mol) / 1000 = -5.76 kJ/mol
Finally, let's adjust for the heat absorbed by the calorimeter:
ΔU = ΔU + CΔT = -5.76 kJ/mol + 4.90 kJ/°C * (29.00-25.00) °C = -7.68 kJ/mol
Since the enthalpy change is negative (indicating an exothermic process), and is larger than the magnitude of the heat released by sucrose alone, we can eliminate choices B and D. Additionally, the magnitude of the enthalpy is closer to choice A than choice C. Therefore, the best choice is A.

The Temperature Rises from 25