A student dissolves 5.00 g of NH4NO3 (M = 80.04 g/mol) in 100.0 g of water in a coffee-cup calorimeter. Initial water temperature = 22.0 C. After dissolution and complete mixing, the minimum temperature is 18.6 C. Specific heat of solution = 4.18 J/(g*C). Total mass of solution = 105.0 g. Calorimeter heat capacity is negligible.
What is the molar heat of solution of NH4NO3?
- Acheck_circle
+23.9 kJ/mol
- B
+1.49 kJ/mol
- C
-23.9 kJ/mol
- D
-1.49 kJ/mol
Explanation
q_soln = m<em>c</em>deltaT = 105.0 * 4.18 * (-3.4) = -1492 J (lost by solution). Heat absorbed by reaction = +1492 J. mol = 5.00/80.04 = 0.0625. delta H_soln = 1492/0.0625 = 23,900 J/mol = +23.9 kJ/mol (endothermic).