A student dissolves 4.00g of solid NH4NO3 in 100.0g of water that is initially at 25.0∘C. The solution is stirred in an insulated calorimeter until all of the salt dissolves, and the final temperature of the solution is 21.6∘C. Assume the specific heat capacity of the solution is the same as that of pure water, 4.18Jg−1∘C−1, and neglect the heat capacity of the calorimeter itself.
(a) Calculate the quantity of heat, in joules, that is absorbed from the water during the dissolution process.
(b) Determine the molar enthalpy change for dissolving NH4NO3 under the experimental conditions. Express your answer in kJmol−1 with the appropriate sign.
(c) Given that the molar enthalpy of fusion of ice at 0∘C is 6.01kJmol−1, compare the magnitude of the enthalpy of dissolution you calculated in part (b) with this value. Based on the comparison and on the types of interactions altered, decide whether the dissolution of NH4NO3 should be classified primarily as a physical change, a chemical change, or as having characteristics of both. Provide a clear justification.