A sample of 8.0 g of NH 4 NO 3 (molar mass 80 g/mol) was dissolved in 142 g of water in a calorimeter whose heat capacity is 60 J/K. The temperature fell by 5.0 K. Take the specific heat capacity of t

Question

A sample of 8.0 g of NH 4 NO 3 (molar mass 80 g/mol) was dissolved in 142 g of water in a calorimeter whose heat capacity is 60 J/K. The temperature fell by 5.0 K. Take the specific heat capacity of the final solution as 4.0 J/K-g. ΔH (in kJ/mol) for dissolving NH 4 NO 3 in water is

TestHub · Accepted Answer

The number of moles is calculated as 8.0/80 = 0.10 mol. The total mass of the solution is 142 + 8.0 = 150 g.

The heat absorbed by the solution and calorimeter is given by:

(150 × 4.0 + 60) × 5.0 = 660 × 5.0 = 3300 J

Per mole, this value is 3300/0.10 = 33000 J, which converts to 33.0 kJ/mol.

Since the temperature decreased, the enthalpy change (ΔH) is positive, indicating an endothermic process. Therefore, ΔH = +33.0 kJ/mol. This corresponds to option (b).

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