R1.2 Energy cycles in reactions (HL)
13 revision questions with answers for R1.2 Energy cycles in reactions (HL). Read them here, or play the set as a class game on the projector. Free to host, and students join with a code.
Enthalpy change making 1 mol of a compound from its elements in their standard states?
- Enthalpy of combustion
- Enthalpy of atomisation
- Enthalpy of formationRight answer
- Lattice enthalpy
What this set covers
Energy cycles at HL: enthalpies of formation, combustion, atomisation and lattice enthalpy, calculating ΔH from formation data, and building a Born–Haber cycle with electron affinities and ionisation energies.
- Common mix-up
- Students often assume electron affinity is always exothermic: the second electron affinity of oxygen is endothermic because the electron is added to a negative ion.
- Revision tip
- Write out a Born–Haber cycle for an ionic solid in order, naming each step, then explain why higher charge and smaller radius give larger lattice enthalpy.
All 13 questions and answers
Enthalpy change making 1 mol of a compound from its elements in their standard states?
Answer: Enthalpy of formation
Enthalpy change when 1 mol of a substance burns completely in oxygen?
Answer: Enthalpy of combustion
ΔHf⦵ of O₂(g)?
Answer: 0 kJ mol⁻¹
Expression for ΔH⦵ from enthalpies of formation?
Answer: ΣΔHf(products) − ΣΔHf(reactants)
Expression for ΔH⦵ from enthalpies of combustion?
Answer: ΣΔHc(reactants) − ΣΔHc(products)
ΔHf⦵: C₂H₄ +52, C₂H₆ −84 kJ mol⁻¹. ΔH⦵ for C₂H₄ + H₂ → C₂H₆?
Answer: −136 kJ mol⁻¹
Enthalpy change when 1 mol of an ionic solid separates into gaseous ions?
Answer: Lattice enthalpy
Sign of lattice enthalpy as the IB defines it?
Answer: Positive
Energy cycle used to find the lattice enthalpy of an ionic compound?
Answer: Born–Haber cycle
Enthalpy change for Na(s) → Na(g)?
Answer: Enthalpy of atomisation
Enthalpy of atomisation of chlorine, given Cl–Cl bond enthalpy 242 kJ mol⁻¹?
Answer: +121 kJ mol⁻¹
The second electron affinity of oxygen, O⁻(g) + e⁻ → O²⁻(g), is…?
Answer: Endothermic
Lattice enthalpy is largest for ions with…?
Answer: Higher charge, smaller radius
Play it as a class game
Play this set opens it in splycr, where you can host it for your class straight away. Hosting needs no account: put the room code on the projector, and students join from a phone with the code and their first name. Each question plays as multiple choice, and the three wrong options were written for that question.