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!

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.