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

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!