A student dissolves 9.65 g of ammonium nitrate, NH₄NO₃(s), in 150.0 g of water in a styrofoam coffee-cup calorimeter that is open to the atmosphere. The initial temperature of the water is 24.0 °C, and after the salt has completely dissolved the final temperature is 17.1 °C. Assume the solution has the same specific heat capacity and density as pure water (4.18 J g⁻¹ °C⁻¹ and 1.00 g mL⁻¹, respectively).
(a) Calculate the quantity of heat q (in kJ) exchanged between the aqueous solution and the surroundings during the dissolution.
(b) Determine the molar enthalpy change ΔH (in kJ mol⁻¹) for the dissolution of NH₄NO₃ based on the data collected.
(c) State the sign of ΔH and relate it to the observed temperature change of the water.
(d) Explain why the assumption that the calorimeter itself absorbs negligible heat is reasonable or not in this experiment.