amazon.co.ukEnergetics
A-Level Chemistry revision: Energetics. Learning objectives, key points, worked examples and practice questions across AQA, Edexcel, OCR, WJEC and CCEA.
π Key Points
Key Fact: Standard conditions: 100 kPa, 298 K, 1 mol dmβ»^3; DeltaH_f deg elements = 0
Key Fact: Hess: DeltaH_total = Ξ£DeltaH_steps (path independent); Cycle: formation = atomisation + ionisation + electron affinity + lattice
Key Fact: Born-Haber: DeltaH_f deg = DeltaH_atom + Ξ£IE + Ξ£EA + DeltaH_lattice (for ionic compounds)
Key Fact: Bond enthalpies: DeltaH = Ξ£(bonds broken) - Ξ£(bonds formed); mean values, gaseous only
Key Fact: Solution: DeltaH_soln = DeltaH_lattice + DeltaH_hydration; hydration exothermic
Key Fact: Energy level diagrams: reactants -> products; exo: products lower; endo: products higher
π― Learning Objectives
- Define standard enthalpy changes: formation, combustion, neutralisation, atomisation
- Apply Hess's Law to calculate enthalpy changes
- Use Born-Haber cycles for lattice enthalpies
- Calculate enthalpy changes from bond enthalpies
- Understand enthalpy of solution and hydration
- Use mean bond enthalpies and their limitations
- Interpret energy level diagrams
π‘ Worked Example
Exam-Style Question
Question: Use Born-Haber cycle to calculate lattice enthalpy of NaCl given: DeltaH_f deg (NaCl) = -411, DeltaH_at(Na)=+107, DeltaH_at(Cl)=+122, IE(Na)=+496, EA(Cl)=-349 kJ/mol
Model Answer:
DeltaH_f = DeltaH_at(Na) + DeltaH_at(Cl) + IE(Na) + EA(Cl) + LE. -411 = 107 + 122 + 496 - 349 + LE -> LE = -411 - 376 = -787 kJ/mol. Lattice enthalpy = +787 kJ/mol (endothermic to break)
β Practice Questions
Questions:
- Define standard enthalpy of combustion
- Calculate DeltaH for reaction using bond enthalpies: Hβ + Clβ -> 2HCl
- Why are mean bond enthalpies less accurate than formation data?
- Explain trend in hydration enthalpy down Group 1
- Sketch energy profile for exothermic reaction with catalyst
π¬ Video Resources
- Energetics - Overview -- YouTube Search
- Energetics - Exam Questions -- YouTube Search
π Past Papers & Exam Resources
π Further Reading & Resources
- Physics & Maths Tutor - Energetics -- Free notes, worksheets, and past paper questions by topic
- Dr Frost Maths - Energetics -- Free resources, slides, and interactive questions
- BBC Bitesize - Energetics -- BBC Bitesize revision resources
π Lesson Plan (50 minutes)
- Starter (5 min): Recall prior knowledge of energetics with quick questions.
- Teaching (15 min): Work through each of the learning objectives, explaining principles step by step.
- Key points review (5 min): Revisit the key points together, confirming understanding.
- Worked example (10 min): Model the example question: Use Born-Haber cycle to calculate lattice enthalpy of NaCl given: DeltaH_f deg (NaCl) = -411, DeltaH_at(Na)=+107, DeltaH_at(Cl)=+122, IE(Na)=+496, EA(Cl)=-349 kJ/mol. Solution: DeltaH_f = DeltaH_at(Na) + DeltaH_at(Cl) + IE(Na) + EA(Cl) + LE. -411 = 107 + 122 + 496 - 349 + LE -> LE = -411 - 376 = -787 kJ/mol. Lattice enthalpy = +787 kJ/mol (endothermic to break)
- Practice (10 min): Students attempt the practice questions independently; circulate and support.
- Plenary (5 min): Review answers and address misconceptions.
π Homework
- Define standard enthalpy of combustion
- Calculate DeltaH for reaction using bond enthalpies: Hβ + Clβ -> 2HCl
- Why are mean bond enthalpies less accurate than formation data?
- Explain trend in hydration enthalpy down Group 1
- Sketch energy profile for exothermic reaction with catalyst
π§Ύ Assessment
Check practice answers against the model answer; use the built-in practice questions as formative assessment.