Energetics II | Edexcel A-Level Chemistry (9CH0)
Energetics II
- 70 questions
- 4 subtopics
- Paper 1: advanced inorganic and physical chemistry
- Paper 1 and Paper 3
Covers lattice energy and the Born-Haber cycle, why theoretical and experimental values differ, entropy and the direction of change, and Gibbs free energy as the test of feasibility..
It covers lattice energy, born-Haber cycles and electron affinity, entropy and the direction of change and gibbs free energy and thermodynamic feasibility.
Sample questions from Energetics II
Answer each one closed book first, then open the answer.
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Lattice energy
When calculating the enthalpy change of solution, why must you consider more than one enthalpy of hydration value?
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Separate enthalpy of hydration values exist for cations and anions, and both must be considered when calculating the overall enthalpy change of solution. -
Lattice energy
Why is the enthalpy of hydration of Al³⁺ more exothermic than that of Na⁺?
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Al³⁺ has a higher charge and smaller radius, giving it a much higher charge density, which results in stronger ion-dipole interactions with water. -
Born-Haber cycles and electron affinity
State the Hess's law relationship used to find lattice energy from a Born-Haber cycle.
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The enthalpy of formation equals the sum of the atomisation enthalpies, the ionisation energies and the electron affinities, plus the lattice energy. Rearranging gives the lattice energy. -
Born-Haber cycles and electron affinity
What does a large difference between the experimental and theoretical lattice energies tell you?
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That the bonding has significant covalent character, because the real lattice is more stable than the ionic model predicts. Silver iodide is an example. -
Entropy and the direction of change
Why does ammonium nitrate dissolve spontaneously in water despite the process being endothermic?
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The disruption of the ionic lattice and dispersal of ions causes a favourable entropy increase that drives the spontaneous process. -
Entropy and the direction of change
What values are needed to calculate the entropy change of a system?
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The sum of the standard entropies of the products and the sum of the standard entropies of the reactants. -
Gibbs free energy and thermodynamic feasibility
What condition for Gibbs free energy indicates that a reaction is thermodynamically feasible?
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The Gibbs free energy change must be negative (ΔG < 0). -
Gibbs free energy and thermodynamic feasibility
If a reaction has a positive Gibbs free energy value, what does this indicate about the position of equilibrium?
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The equilibrium constant is small, meaning reactants are favoured at equilibrium.
The 4 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Lattice energy | The two definitions of lattice energy, enthalpy changes of hydration and of solution, how ionic charge and radius set the size of lattice and hydration enthalpies, calculating the enthalpy change of solution for sodium chloride and magnesium chloride, and measuring one in the laboratory. | 19 |
| Born-Haber cycles and electron affinity | First and second electron affinities and atomisation enthalpy, building Born-Haber cycles for sodium chloride and magnesium chloride to find lattice energy, the perfect ionic model and what agreement with experimental values shows, and how polarisation gives covalent character. | 18 |
| Entropy and the direction of change | Recall questions on what entropy measures, on comparing the entropy of solids, liquids and gases, and on calculating the entropy change of a system and of its surroundings. | 19 |
| Gibbs free energy and thermodynamic feasibility | Recall questions on the Gibbs equation, on what makes a reaction feasible, on finding the temperature at which it becomes so, and on why a feasible reaction may still be slow. | 14 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
Edexcel A-Level Chemistry Active Recall Guide
Every topic, not just this one. 1,534 questions with their answers.