4CH1

Energetics

Physical Chemistry · 3 question types

Practise

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 7% of your exam marks.

stable
Low
Stable7%

Calorimetry calculations and energy profile diagrams appear in nearly every series.

Goal of the practical

  • Use a polystyrene-cup calorimeter to record how the temperature of a neutralisation reaction varies with the volume of one reactant added, and use the data to identify the volume that gives the largest temperature change

Apparatus

  • 100 cm³ polystyrene cup with a fitted lid
  • Thermometer (0–110 °C, 0.5 °C divisions) and stirring rod
  • 25 cm³ measuring cylinder (×2: one for each reactant)
  • 25 cm³ dilute sodium hydroxide solution per run
  • Dilute hydrochloric acid (same concentration as the alkali)
Polystyrene-cup calorimeter for the practical: two nested styrofoam cups holding the reaction mixture, a styrofoam cover, a thermometer and a stirrer
Source: Temperature change practical by Save My Exams

Method

  • Measure 25 cm³ of NaOH solution into the polystyrene cup and place on the bench in the cup-and-lid assembly
  • Read the temperature once it has settled — this is Tstart
  • Measure 5 cm³ of HCl with the second measuring cylinder, add it to the cup, fit the lid, and stir gently with the thermometer
  • Read the highest temperature reached — this is Tmax
  • Empty and dry the cup, then repeat the run with 10 cm³ of HCl, then 15, 20, 25, 30 and 35 cm³ — stepping past the expected equivalence point so the peak of the curve can be seen clearly

Sample results table

Volume of HCl added / cm³Start temp / °CFinal temp / °CΔT / °C
521.022.6+1.6
1021.024.0+3.0
1521.024.8+3.8
2021.025.4+4.4
2521.026.0+5.0
3021.025.4+4.4
3521.024.6+3.6
  • Plot ΔT (y-axis) against volume of HCl added (x-axis) and draw a smooth curve
  • The peak of the graph indicates the volume of HCl at which the largest temperature rise occurs — for equal concentrations of acid and alkali this should be at 1 : 1 stoichiometry (25 cm³ in this example)
  • Past the peak, additional acid cools the mixture relative to the maximum because the extra acid is not warming up further but is mixing in at room temperature