A student dissolves 11.5 g of ammonium nitrate (NH4NO3) in 200g of water in a well-insulated open cup. He then observes the temperature of the water fall from 23.0 °C to 18.0 °C over the course of 6.1 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: NH4NO3(s) → NH4(aq) + NO3 (aq)

Requied:
a. Is this reaction exothermic, endothermic, or neither?
b. Calculate the reaction enthalpy ΔHrxn per mole of NH4NO3.