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14 November, 14:42

How much potassium nitrate has to dissolve in water to absorb 105 kj of heat? there are 4.184 kj/kcal. also note the answer is to be reported in kg?

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  1. 14 November, 14:45
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    Lattice energy of potassium nitrate (KNO3) = - 163.8 kcal/mol

    Hydration energy of KNO3 = - 155.5 kcal/mole

    Heat of solution is the amount of heat absorbed by water when 1 mole of KNO3 is dissolved in it

    Heat of solution = Hydration energy - Lattice energy

    = - 155.5 - (-163.8) = 8.3 kcal/mol

    1 kcal/mol = 4.184 kJ/mole

    Therefore, 8.3 kcal/mole = 4.184 * 8.3 = 34.73 kJ/mol

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

    The given 105 kJ of heat would correspond to : 105/34.73 = 3.023 moles of KNO3

    Molar mass of KNO3 = 101.1 g/mole

    Mass of KNO3 = Molar mass * moles

    = 101.1 * 3.023 = 305.63 g = 0.3056 kg
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