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6 July, 22:05

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 101 kJ of heat?

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Answers (1)
  1. 6 July, 22:18
    0
    293.99 g

    OR

    0.293 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 = 101kJ

    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 101 kJ of heat would be

    = 101/34.73

    = 2.908 moles of KNO3

    Molar mass of KNO3 = 101.1 g/mole

    Mass of KNO3 = Molar mass x moles

    = 101.1 g/mole x 2.908

    = 293.99 g

    = 0.293 kg

    293.99 g potassium nitrate has to dissolve in water to absorb 101 kJ of heat.
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