When of potassium nitrate is added to of water in a coffee-cup calorimeter

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

When

5.00\,\text{g}

of potassium nitrate is added to

100.0\,\text{g}

of water in a coffee-cup calorimeter, the temperature of the aqueous solution falls from

24.0\,^{\circ}\text{C}

18.4\,^{\circ}\text{C}

. Assume that the specific heat capacity of the solution is

4.18\,\text{J}\,\text{g}^{-1}\,^{\circ}\text{C}^{-1}

and that heat losses to the surroundings are negligible. The molar mass of potassium nitrate is

101.1\,\text{g}\,\text{mol}^{-1}

. (a) Calculate the heat

q_{\text{solution}}

associated with the temperature change of the solution. Report the value with the correct sign and units. (b) Using your answer to part (a), determine the enthalpy change per mole of potassium nitrate that dissolves under these conditions. Express the result in

\text{kJ}\,\text{mol}^{-1}

with the proper sign. (c) Explain why the sign of

\Delta H_{\text{dissolution}}

obtained in part (b) is consistent with the observed temperature change.

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