Energetics

EasyMedium
12345678910111213141516171819202122232425262728
Question 9
Medium

An anhydrous lithium chloride salt, LiCl\text{LiCl}LiCl, is dissolved in water in a simple calorimeter to determine its enthalpy of solution.

A student uses the following method:

  • Measure 60.0 cm360.0\text{ cm}^360.0 cm3 of distilled water into a polystyrene cup.
  • Record the initial temperature of the water.
  • Add 2.12 g2.12\text{ g}2.12 g of anhydrous LiCl\text{LiCl}LiCl and stir.
  • Record the highest temperature reached.

Results:

  • Initial temperature: 20.2 ∘C20.2\ ^\circ\text{C}20.2 ∘C
  • Highest temperature reached: 28.2 ∘C28.2\ ^\circ\text{C}28.2 ∘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 LiCl\text{LiCl}LiCl: 42.4 g mol−142.4\text{ g mol}^{-1}42.4 g mol−1
a.

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

[5]
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