Question

When a solid dissolves in water, heat may be evolved or absorbed. The heat of dissolution (dissolving) can be determined using a coffee cup calorimeter. In the laboratory a general chemistry student finds that when 24.22 g of BaBr2(s) are dissolved in 118.20 g of water, the temperature of the solution increases from 24.85 to 28.18 °C. The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.84 J/°C. Based on the student's observation, calculate the enthalpy of dissolution of BaBr2(s) in kJ/mol. Assume the specific heat of the solution is equal to the specific heat of water.

Answer 1

To calculate the enthalpy of dissolution of BaBr2(s) in kJ/mol, we can use the equation q = -mCΔT. By substituting the given values and calculating the heat transferred, we then divide by the moles of BaBr2(s) dissolved to find the enthalpy of dissolution. The enthalpy of dissolution of BaBr2(s) is approximately -18.5 kJ/mol.

Step-by-step explanation:

To calculate the enthalpy of dissolution of BaBr2(s) in kJ/mol, we need to use the equation:

q = -mCΔT

Where q is the heat transferred, m is the mass of the solution, C is the specific heat of the solution, and ΔT is the change in temperature of the solution.

First, we need to calculate the mass of the solution. This is done by adding the mass of the BaBr2(s) to the mass of water:

mass of solution = mass of BaBr2(s) + mass of water

mass of solution = 24.22 g + 118.20 g = 142.42 g

Next, we calculate the heat transferred:

q = -mCΔT

q = -(142.42 g)(4.18 J/g °C)(28.18 °C - 24.85 °C)

q = -1987.87 J

Finally, we convert the heat transferred to kJ/mol by dividing by the moles of BaBr2(s) dissolved:

moles of BaBr2(s) = mass of BaBr2(s) / molar mass of BaBr2

moles of BaBr2(s) = 24.22 g / (137.33 g/mol + 2(79.90 g/mol))

moles of BaBr2(s) = 0.1072 mol

enthalpy of dissolution = q / moles of BaBr2(s)

enthalpy of dissolution = -1987.87 J / 0.1072 mol = -18514.92 J/mol

Therefore, the enthalpy of dissolution of BaBr2(s) is -18514.92 J/mol or -18.5 kJ/mol.