A 10.0 g sample of solid NH4NO3 (M = 80.05) is added to 100.0 g H2O in a well-insulated container. B — Thermochemistry Chemistry Question

A 10.0 g sample of solid NH₄NO₃ (M = 80.05) is added to 100.0 g H₂O in a well-insulated container. Both the solid and the water are initially at 24.00 ºC, but after the NH₄NO₃ dissolves, the temperature of the mixture is 17.11 ºC. What is ∆Hºrxn for the dissolution of NH₄NO₃(s)? Assume that the specific heat capacity of the NH₄NO₃ solution is the same as that of pure water, 4.184 J g^-1 ºC^-1.