A-LevelChemistryChemical energetics9701/42 · Oct/Nov 2025 · Q46 Marks
Define enthalpy change of atomisation, ∆Hat.
- (a)Define enthalpy change of atomisation, ∆Hat.[1]
- (b)Define first electron affinity, EA.[1]
- (c)Explain why the first electron affinity of chlorine is more exothermic than the first electron affinity of iodine.[2]
- (d)The enthalpy change for the reaction Cl2(g) + 2e– → 2Cl–(g) is –486 kJ mol–1. The first electron affinity of chlorine is –364 kJ mol–1. Calculate the enthalpy change of atomisation of chlorine.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.
- [1] energy required when one mole of gaseous atoms is formed from the element
- [1] energy released when one mole of gaseous atoms gains one mole of electrons and becomes one mole of gaseous 1- ions
- [1] M1: iodine atom has greater radius
- [1] M2: less attraction between nucleus and incoming electron in iodine
- [1] M1: ½ (–486 + (2 × 364))
- [1] M2: +121
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