Energetics

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Question 4
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A student performs a calorimetry experiment to determine the enthalpy of solution of ammonium chloride, NH4Cl\text{NH}_4\text{Cl}NH4​Cl.

The student uses the following method:

  • Measure 50.0 cm350.0\text{ cm}^350.0 cm3 of distilled water into a polystyrene cup.
  • Record the initial temperature of the water.
  • Add 5.35 g5.35\text{ g}5.35 g of solid NH4Cl\text{NH}_4\text{Cl}NH4​Cl and stir.
  • Record the lowest temperature reached.

Results:

  • Initial temperature: 21.4 ∘C21.4\ ^\circ\text{C}21.4 ∘C
  • Lowest temperature: 15.4 ∘C15.4\ ^\circ\text{C}15.4 ∘C

Constants & Assumptions:

  • Specific heat capacity of the solution: c=4.18 J K−1 g−1c = 4.18\text{ J K}^{-1}\text{ g}^{-1}c=4.18 J K−1 g−1
  • Density of the solution: 1.00 g cm−31.00\text{ g cm}^{-3}1.00 g cm−3
  • Molar mass of NH4Cl\text{NH}_4\text{Cl}NH4​Cl: 53.5 g mol−153.5\text{ g mol}^{-1}53.5 g mol−1
a.

Calculate the enthalpy of solution, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, for ammonium chloride in this experiment. Give your answer to 3 significant figures.

[4]
b.

The uncertainty in each temperature reading from the thermometer is ±0.15 ∘C\pm0.15\ ^\circ\text{C}±0.15 ∘C. Calculate the percentage uncertainty in the temperature change for this experiment.

[2]

Energetics Questions

  1. A Level
  2. /Chemistry
  3. /Energetics