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20 April, 11:05

Potassium nitrate has a lattice energy of - 163.8 kcal/mol and a heat of hydration of - 155.5 kcal/mol. How much potassium nitrate has to dissolve in water to absorb 113 kJ of heat?

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  1. 20 April, 11:28
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    0.328 kg

    Explanation:

    Given dа ta:

    Lattice energy of Potassium nitrate (KNO3) = - 163.8 kcal/mol

    Heat of hydration of KNO3 = - 155.5 kcal/mol

    Heat to absorb by KNO3 = 113kJ

    To find:

    Mass of KNO3 to dissolve in water = ?

    Solution:

    Heat of solution = Hydration energy - Lattice energy

    = - 155.5 - (-163.8)

    = 8.3 kcal/mol

    We already know,

    1 kcal/mol = 4.184 kJ/mole

    Therefore,

    = 4.184 kJ/mol x 8.3 kcal/mol

    = 34.73 kJ/mol

    Now, 34.73 kJ of heat is absorbed when 1 mole of KNO3 is dissolved in water.

    For 113 kJ of heat would be

    = 113/34.73

    = 3.253 moles of KNO3

    Molar mass of KNO3 = 101.1 g/mole

    Mass of KNO3 = Molar mass x moles

    = 101.1 g/mole x 3.253

    = 328.87 g

    = 0.328 kg

    328.8 g potassium nitrate has to dissolve in water to absorb 113 kJ of heat.
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