The dissolution of ammonium nitrate in water is commonly used in instant cold packs. In a laboratory investigation a student dissolves 3.20g of crystalline NH4NO3 in 75.0g of water contained in an insulated cup. The temperature of the water drops from 22.0∘C to 17.4∘C during the process. Assume that the specific heat capacity of the solution is 4.18Jg−1∘C−1 and that the calorimeter absorbs a negligible amount of heat.
(1) Calculate the heat absorbed by the aqueous surroundings during the dissolution.
(2) Determine the molar enthalpy change, ΔHdiss, for the dissolution of NH4NO3 expressed in kJmol−1.
(3) State whether the dissolution process is endothermic or exothermic and justify your answer based on both the calculated heat and the observed temperature change.