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IB Chemistry HL 1.4.2 Hl Gibbs Energy G Questions

Use real HL exam questions to calculate Gibbs energy from enthalpy and entropy, track kelvin and unit conversions and interpret the resulting sign.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Calculate ΔG° from ΔH° − TΔS° using kelvin temperature, consistent energy units and the correct sign convention.
  • Use ΔH°, ΔS° and temperature to predict how the sign or magnitude of ΔG° changes and identify the relevant temperature dependence.
  • Interpret the sign and magnitude of ΔG° as the thermodynamic tendency or energy availability of the reaction, without substituting an unsupported equilibrium claim.

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Study 1.4.2 (HL)—Gibbs energy (ΔG) conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Chemistry HL 1.4.2 Hl Gibbs Energy G Questions question 1

[Maximum number: 2]

Nitrous acid, HNO2\mathrm{HNO}_{2}, is a weak acid which can be used to make acidic buffers.

The overall reaction for the synthesis of ethyl ethanoate from ethane is:

2C2H6( g)+Cl2( g)+32O2( g)→C4H8O2( g)+2HCl( g)+H2O( g)2 \mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})+\frac{3}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}(\mathrm{~g})+2 \mathrm{HCl}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

Calculate the Gibbs energy change, ΔGθ\Delta G^{\theta} in kJmol−1\mathrm{kJ} \mathrm{mol}^{-1}, for this reaction under standard conditions. Use the value of −4 kJ mol−1-4 \mathrm{~kJ} \mathrm{~mol}^{-1} for ΔHθr\Delta H^{\theta}{ }_{\mathrm{r}} and your answer from (d)(iv). If you did not obtain an answer for (d)(iv) use −10JK−1 mol−1-10 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}, although this is not the correct answer. Use sections 1 and 4 of the data booklet.

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