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CAIE A Level Chemistry 9701 · Chemical energetics

Chemical energetics: explain question

Explain4 marksStandard

The Born-Haber cycle for an ionic compound is used to determine its lattice energy. The lattice energy is the energy change when one mole of an ionic compound is formed from its gaseous ions. In a Born-Haber cycle, the lattice energy is calculated using other enthalpy changes, such as the enthalpy change of atomisation and the first electron affinity.

Explain what is meant by the enthalpy change of atomisation and the first electron affinity, and explain how the lattice energy of an ionic compound is related to the sizes of the ions.

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4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.

Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.

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