Unit 4: Reactivity 1: What Drives Chemical Reactions?
Topic 4.2: Energy Cycles in Reactions Questions
Practice 20 exam-style questions for IB Chemistry Topic 4.2. Review the question stems below, then unlock the full Question Bank to access markschemes, model answers, and AI grading.
1Identify1 mark
Identify the process represented by the step Na(g) -> Na+(g) + e- in a Born-Haber cycle.
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Using Hess's law and the enthalpies of combustion below, determine the enthalpy change for the hydrogenation of ethene to ethane.
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Calculate the standard enthalpy change for the combustion of ethanol, C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l), using Δ⊖: C₂H₅OH(l) = −277.0, CO₂(g) = −393.5, H₂O(l) = −285.8 kJ mol⁻¹.
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Unlock Question4Draw2 marks
2026
Draw a Born-Haber cycle for the formation of sodium chloride.
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Determine the lattice enthalpy of lithium chloride, LiCl(s) → Li⁺(g) + Cl⁻(g), using: Δ⊖(LiCl) = −409; ΔHₐₜₒₘ⊖(Li) = +159; ½ bond dissociation of Cl₂ = +121; 1st IE(Li) = +520; 1st EA(Cl) = −349 (all kJ mol⁻¹).
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2026
Which equation represents the standard enthalpy of formation of methane?
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2026
In a Born-Haber cycle, which step is always endothermic?
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2026
Using bond enthalpies H–H 436, Cl–Cl 242 and H–Cl 431 kJ mol⁻¹, what is ΔH for H₂ + Cl₂ → 2HCl?
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2026
Outline why bond enthalpy calculations give only approximate enthalpy changes.
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2026
Explain why the standard enthalpy of formation of an element in its standard state is zero.
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Unlock Question12calculate3 marks
Use bond enthalpies to calculate ΔH for H₂ + Cl₂ → 2HCl. (E(H-H) = 436, E(Cl-Cl) = 243, E(H-Cl) = 431 kJ mol⁻¹)
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Unlock Question13explain3 marks
Explain why enthalpy changes calculated from bond enthalpies are only approximate.
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Unlock Question14define3 marks
Define average bond enthalpy, and state whether bond breaking is endothermic or exothermic.
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Unlock Question15predict2 marks
Predict, using bond enthalpies, whether a reaction is exothermic when the bonds formed in the products are stronger than those broken in the reactants, and explain your reasoning.
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State why Hess's law allows an enthalpy change to be found without carrying out the reaction directly.
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Calculate the standard enthalpy change for the hydrogenation of propene to propane using the standard enthalpies of formation below.
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State two reasons why an enthalpy change calculated from average bond enthalpies differs from one calculated from enthalpies of formation.
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Determine the lattice enthalpy of potassium chloride from the Born-Haber data below.
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