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15 April, 11:46

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.

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  1. 15 April, 14:24
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    The enthalpy of dissolution of BaBr2 (s) is - 8,94 kJ/mol

    Explanation:

    In a dissolution process, the heat is released, so it must be negative (-)

    The same to ΔH.

    Q = m. C. ΔT

    Q = 118,2 g. 1,84 J/g°C. (Tfinal - Tinitial)

    Q = 118,2 g. 1,84 J/g°C. (28,18°C - 24,85°C)

    Q = 118,2 g. 1,84 J/g°C. 3,33°C

    Q = 724,2 J

    724,2 J / 1000 = 0,7242 kJ

    We dissolved 24,22g of BaBr2

    Molar mass BaBr2: 297,13 g/m

    We dissolved 24,22 g / 297,13 g/m = 0,081 moles

    ΔH = kJ/mol

    ΔH = - 0,7242 kJ / 0,081 mol

    ΔH = - 8,94kJ/mol
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