Dissolution process of an ionic compound such as ammonium nitrate, NH NO3, is wa
ID: 1033403 • Letter: D
Question
Dissolution process of an ionic compound such as ammonium nitrate, NH NO3, is water can be represented by the following equation: NH4NO3(aq) NH4(aq) + NO3 (aq) When a 10.0-g sample of solid ammonium nitrate is added to 100.0 g of water in a Styrofoam calorimet and completely dissolved, the temperature of the solution drops from 24.0 °C to 17.4°C (a) Is the dissolution of ammonium nitrate an endothermic or exothermic process? Explain. (b) Calculate heat gained/lost by: (1) water, and (i) the calorimeter. (Specific heat of water is 4.184 J/g. C; heat capacity of calorimeter is 15 J/PC). (c) What is the total amount of heat (in Joules) gained/lost by the system (the dissolution of NH,NO). (d) Calculate the molar enthalpy of dissolution (AHiss; in kJ/mol) for ammonium nitrate.Explanation / Answer
(a)
Since the temp. of the solution drops, this means that the reaction absorbs heat from the surroundings, this means that the reaction is endothermic.
(b)
Heat lost by water = m*C*dT = 100*4.184*(24-17.4) = 2761.44 J
Heat lost by calorimeter = c*dT = 15*(24-17.4) = 99 J
(c)
Total heat lost by the system = 2761.44+99 = 2860.44 J
(d)
Moles of solute = Mass/MW = 10/80 = 0.125
So,
Molar enthalpy = 2860.44/0.125 = 22.883 kJ/mol
Hope this helps !