Chemical Energetics

Worked examples (6)

• 1Exothermic vs endothermic (2 marks)
• 2Defining enthalpy of formation (2 marks)
• 3ΔH from bond energies (4 marks)
• 4ΔH of combustion by calorimetry (4 marks)
• 5Enthalpy of neutralisation (4 marks)
• 6Why bond-energy ΔH differs from experiment (3 marks)

Worked examples (6)

• 1Stating and using Hess's law (2 marks)
• 2ΔHr from formation data (2 marks)
• 3ΔHr from formation data, full cycle (3 marks)
• 4ΔHf from combustion data (4 marks)
• 5ΔHc from formation data (4 marks)
• 6ΔHr of hydrogenation from combustion data (4 marks)

Worked examples (6)

• 1Defining lattice energy (2 marks)
• 2Terms in a Born–Haber cycle (3 marks)
• 3Lattice energy of NaCl (4 marks)
• 4Comparing lattice energies (3 marks)
• 5Lattice energy of MgCl₂ (4 marks)
• 6Theoretical vs experimental lattice energy (4 marks)

Worked examples (6)

• 1Defining the enthalpies (2 marks)
• 2The solution energy cycle (2 marks)
• 3Calculating ΔHsol (3 marks)
• 4Finding a hydration enthalpy (3 marks)
• 5Explaining hydration-enthalpy trends (4 marks)
• 6Explaining solubility (4 marks)

Worked examples (6)

• 1Sign of ΔS for state changes (2 marks)
• 2Sign of ΔS for a reaction (2 marks)
• 3Calculating ΔS° (3 marks)
• 4ΔS° for the Haber reaction (3 marks)
• 5Entropy of dissolving (4 marks)
• 6Why endothermic reactions can occur (4 marks)

Worked examples (5)

• 1The feasibility criterion (2 marks)
• 2Calculating ΔG (3 marks)
• 3Temperature for feasibility (3 marks)
• 4Feasibility and the four sign cases (4 marks)
• 5Temperature limit on a yield (4 marks)