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In the laboratory a general chemistry student finds that when 2.00 g FeBr3(s) is dissolved in 119.40 g water, the temperature of the solution increases from 22.80 to 24.78 °c. the heat capacity of the calorimeter was determined in a separate experiment to be 1.66 J/°C. Based on the student's observation, calculate the dissolution enthalpy of FeBr3(s) in kj/mol.
Accepted Answer
The dissolution enthalpy of FeBr3(s) can be calculated using the following steps:
1. Calculate the heat absorbed by the solution:
ΔT = 24.78 °C - 22.80 °C = 1.98 °C
q_solution = m_solution
C_solution
ΔT
Assuming the specific heat capacity of the solution is similar to that of water (4.18 J/g°C), we get:
q_solution = (119.40 g + 2.00 g)
4.18 J/g°C
1.98 °C ≈ 1000 J
2. Calculate the heat absorbed by the calorimeter:
q_calorimeter = C_calorimeter
ΔT = 1.66 J/°C
1.98 °C ≈ 3.3 J
3. Calculate the total heat absorbed (q_total):
q_total = q_solution + q_calorimeter ≈ 1000 J + 3.3 J ≈ 1003 J
4. Convert the heat absorbed to kJ:
q_total = 1003 J / 1000 J/kJ = 1.003 kJ
5. Calculate the moles of FeBr3:
Molar mass of FeBr3 = 295.56 g/mol
Moles of FeBr3 = 2.00 g / 295.56 g/mol ≈ 0.00677 mol
6. Calculate the dissolution enthalpy (ΔH_dissolution):
ΔH_dissolution = q_total / moles of FeBr3 ≈ 1.003 kJ / 0.00677 mol ≈ 148 kJ/mol
Therefore, the dissolution enthalpy of FeBr3(s) is approximately 148 kJ/mol. Note that this is an endothermic process, as the dissolution is accompanied by an increase in temperature, indicating that heat is absorbed from the surroundings.
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