Question

KNO3(s) --> K+(aq) + NO3-(aq)

This reaction was carried out in a Styrofoam insulated calorimeter and the following data were recorded:

Mass of solid KNO3 dissolved

10.1 g

Mass of aqueous solution (c = 4.18 J/gºC)

100. g

T initial

30.0ºC

T final

21.6ºC

Molar mass of KNO3

101 g/mol

Which of the following equations correctly shows the heat of solution (kJ/mol) for the dissolving of KNO3?



KNO3(s) + 35.1 kJ --> K+(aq) + NO3-(aq)
KNO3(s) +3.51 kJ --> K+(aq) + NO3-(aq)
KNO3(s) --> K+(aq) + NO3-(aq) + 8.4 kJ
KNO3(s) --> K+(aq) + NO3-(aq) + 3510 kJ

Answer 1

Answer:

KNO₃(s) + 35,1 kJ → K⁺(aq) + NO₃⁻(aq)

Explanation:

In the reaction:

KNO₃(s) → K⁺(aq) + NO₃⁻(aq)

The heat absorbed for the reaction (Because the temperature decreases) is:

Q = C×m×ΔT

Where C is specific heat (4,18J/g°C); m is mass (100g); ΔT is (30,0°C-21,6°C = 8,4°C)

Replacing:

Q = 4,18J/g°C×100g×8,4°C

Q = 3511 J

Now, moles of KNO₃ are:

10,1g×(1mol / 101g) = 0,1 moles.

Heat of solution in kJ/mol is:

3,511 J / 0,1 mol = 35,1 kJ

As the heat was absorbed for the reaction, right answer is:

KNO₃(s) + 35,1 kJ → K⁺(aq) + NO₃⁻(aq)

That means the reaction needs the heat to occurs.

I hope it helps!