(a) ΔHproducts>ΔHreactants; (b) endothermic; (c) ionic bonds between NH+4 and NO-3.
Explanation:(a) Enthalpy of formation of reactants and products
We have the reaction
Mr/g⋅mol-1mmmll80.04
mmmmmmmmNH4NO3(s)⇌NH+4(aq)+NO-3(aq)
ΔfH∘/kJ⋅mol-1m-365.1mmmm-132.8mmm-206.6
ΔfH∘reactants=-365.1 kJ.mol
ΔfH∘products=(-132.8 - 206.6) kJ=-339.4 kJ/mol
Moles of NH4NO3=10.0g NH4NO3×1 mol NH4NO380.04g NH4NO3=0.1249 mol NH4NO3=0.1249 mol reaction
ΔHreactants=0.1249mol reaction×-365.1 kJ1mol reaction=-45.6 kJ
ΔHproducts=0.1249mol reaction×-339.4 kJ1mol reaction=-42.4 kJ
∴ ΔHproducts>ΔHreactants
(b) Exothermic or endothermic?
The temperature decreased when the ammonium nitrate dissolved in the water.
Energy left the system, so the reaction is endothermic.
(c) Bonds broken
The ionic bonds between the NH+4 ions and NO-3 ions were broken when the ammonium nitrate dissolved in the water.
