IB Chemistry SL Reactivity 1.1 Measuring Enthalpy Changes

Practise determining reaction enthalpy from temperature measurements and energy profiles. Assign exothermic or endothermic signs, calculate q = mcΔT, convert heat transferred…

Syllabus
First assessment 2025
Topic
1.1
Level
SL

Exam points

  • use temperature change and an energy profile to assign the sign of reaction enthalpy
  • calculate heat transfer with q = mcΔT before converting it to kJ mol⁻¹
  • evaluate heat loss, incomplete combustion or heat-capacity assumptions in calorimetry

Covered syllabus points

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

1.1 Measuring enthalpy changes 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.

1.1 Measuring enthalpy changes question 2

[Maximum number: 1]

Chlorine occurs in Group 7, the halogens.

Chloroethene, H2C=CHCl\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCl}, the monomer used in the polymerization reaction in the manufacture of the polymer poly(chloroethene), PVC, can be synthesized in the following two-stage reaction pathway.

Stage 1: C2H4( g)+Cl2( g)→ClCH2CH2Cl(g)\quad \mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow \mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{Cl}(\mathrm{g})

Stage 2: ClCH2CH2Cl(g)→H2C=CHCl(g)+HCl(g)\quad \mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{Cl}(\mathrm{g}) \rightarrow \mathrm{H}_{2} \mathrm{C}=\mathrm{CHCl}(\mathrm{g})+\mathrm{HCl}(\mathrm{g})

State whether the reaction given in stage 1 is exothermic or endothermic.

1.1 Measuring enthalpy changes question 3

[Maximum number: 3]

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

Figure for Question 1.1 Measuring enthalpy changes question 3 — IB Chemistry SL

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.

Figure for Question 1.1 Measuring enthalpy changes question 3 — IB Chemistry SL
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