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IB Chemistry HL 1.1 Measuring Enthalpy Changes Questions

Practise chemistry energy changes by classifying reactions, reading enthalpy profiles and calculating q and molar ΔH from calorimetry data.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Classify endothermic and exothermic changes from temperature shifts, heat transfer and the sign of ΔH.
  • Draw or interpret enthalpy profiles to compare reactant/product levels, ΔH, stability and activation energy.
  • Calculate q = mcΔT from the solution mass, specific heat capacity and temperature change.
  • Convert calorimetry q to molar ΔH with ΔH = −q/n, correct stoichiometry, sign and kJ mol⁻¹ units.
  • Evaluate calorimetry using density and heat-capacity assumptions, temperature uncertainty and heat-loss evidence.

Covered syllabus points

1.1.1—Energy transfer1.1.2—Endothermic vs. exothermic1.1.3—Stability and energy1.1.4—Standard enthalpy change (ΔH⦵)

Question 1

[Maximum number: 1]

The increased concentration of carbon dioxide in the atmosphere is thought to result from the increased combustion of fossil fuels such as petroleum.

Outline why the energy available from an engine will be less than these theoretical values.

Question 2

[Maximum number: 1]

Two groups of students (Group A and Group B) carried out a project* on the chemistry of some group 7 elements (the halogens) and their compounds.

In the first part of the project, the two groups had a sample of iodine monochloride (a corrosive brown liquid) prepared for them by their teacher using the following reaction.

I2( s)+Cl2( g)→2ICl(l)\mathrm{I}_{2}(\mathrm{~s})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{ICl}(\mathrm{l})

The following data were recorded.

Table for Question 2 — IB Chemistry HL

Using a digital thermometer, the students discovered that the reaction was exothermic. State the sign of the enthalpy change of the reaction, ΔH\Delta H.

Question 3

[Maximum number: 3]

Phenylethene (styrene) is produced from ethylbenzene in a gas-phase equilibrium.

Figure for Question 3 — IB Chemistry HL

The forward reaction is endothermic, uses iron(III) oxide as a catalyst, and takes place at 900 K .

Sketch the energy profile for the reaction, both with and without the catalyst, labelling ΔH\Delta H and the activation energies.

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