Question

When 5.00 g of NH4NO3 is dissolved in 100.0 g of water in a styrofoam cup, the T = - 3.82 ^°C. Is the process of dissolving ammonium nitrate endo- or exothermic? What is the heat of this process in kJ/mol?

Answer 1

Answer:

The process is endothermic.

Heat is 26,9 kJ/mol

Explanation:

The dissolution of NH₄NO₃ in water is:

NH₄NO₃ → NH₄⁺ + NO₃⁻

As the change of temperature in the cup is ΔT = -3,82°C

The process is endothermic. Because the temperature is decreasing in the process. That means the process needs heat.

Assuming the  heat capacity of the solution is 4.18 J/Kg :

q = -C×m×ΔT

Where q is heat, C is heat capacity (4,18J/Kg), m is mass (105g) and ΔT is change in temperature (-3,82°C)

q = 1677 J ≈ 1,68kJ

The moles of NH₄NO₃ dissolved are:

5,00g × (1mol / 80,043g) = 0,0625 moles

That means heat of this process in kJ/ mol is:

1,68kJ / 0,0625moles = 26,9 kJ/mol

I hope it helps!