Instant cold packs contain solid ammonium nitrate and a separate pouch of water. When the pouch is broken the solid dissolves and the pack becomes cold.
NH4NO3(s) + aq → NH4+(aq) + NO3-(aq) ΔH = +25.7 kJ mol-1 ΔS = +108.7 J K-1 mol-1
Calculate ΔG for dissolving ammonium nitrate at 298 K.
[2]
Explain why ammonium nitrate dissolves even though the process is endothermic.
[2]
Calculate the temperature at which ΔG for this process would be zero.
[2]
Suggest why the temperature calculated in part (c) has no practical meaning for a cold pack.
[1]
A cold pack contains 40.0 g of ammonium nitrate (Mr = 80.0). Calculate the heat energy absorbed, in kJ, when all of it dissolves.
[2]